Jean-Marie Gouarné > ODF-lpOD-1.121 > ODF::lpOD::Table

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Module Version: 1.002   Source   Latest Release: ODF-lpOD-1.126

NAME ^

ODF::lpOD::Table - Table management

DESCRIPTION ^

The present manual page introduces the way lpOD allows the user to handle ODF tables and their components, namely the columns, rows and cells.

The lpOD API doesn't make differences between document types in this area. So, tables are dealed with in the same way for a spreadsheet document (whose content is just a set of tables) as for any other document.

A table is an instance of the lpOD odf_table class.

An odf_table object is a structured container that holds two sets of objects, a set of rows and a set of columns, and that is optionally associated with a table style.

The basic information unit in a table is the cell. Every cell is contained in a row. Table columns don't contain cells; an ODF column holds information related to the layout of a particular column at the display time, not content data.

A cell can directly contain one or more paragraphs. However, a cell may be used as a container for high level containers, including lists, tables, sections and frames.

Every table is identified by a name (which must be unique for the document) and may own some optional properties.

Table creation and retrieval ^

Like any other odf_element table may be created either from scratch according to various parameters or by cloning an existing table using the generic clone method of odf_element. The second way is the most recommended one because, while it looks very easy to create a table with a default appearance, a typical convenient layout may require a lot of style definitions and is much more difficult to specify by program than through a point-and-click interface.

A table is created using odf_create_table with a mandatory name as its first argument and the following optional parameters:

Once created, a table may be incorporated somewhere using insert_element of append_element, like any other odf_element.

Caution: a table should not be inserted in any context. For example, a table should not be inserted within a paragraph. A bad placement may corrupt the document structure. Right contexts are, for example, the document body (in a spreadsheet or text document), a section (in a text document) or a table cell (knowing that the ODF standard allows nested tables).

The style of a table may be retrieved or changed at any time using the generic get_style() and set_style() accessors.

A table may be retrieved in a document according to its unique name using the context-based get_table_by_name with the name as argument. It may be selected by its sequential position in the list of the tables belonging to the context, using get_table_by_position, with a zero-based numeric argument (possibly counted back from the end if the argument is negative). A get_table() method is provided, that works like get_table_by_position() if the argument is numeric or like get_table_by_name() otherwise (of course, if the name of the desired table looks like a number, there is no choice but get_table_by_name() to retrieve it by name). Without argument, get_table() returns the first table in the context (if any). In addition, it's possible to retrieve a table according to its content, through get_table_by_content; this method returns the first table (in the order of the document) whose text content matches the given argument, which is regarded as a regular expression.

In addition, an application can get all the tables of a given context using the get_tables() method, without argument.

An application may retrieve a table from any element that belong to it, thanks to the get_parent_table() method. This method returns undef if the calling element is not in a table. Knowing that a paragraph may be included in a table cell and that a table cell indirectly belongs to a table, the following sequence selects a paragraph matching a given expression and, if the paragraph belongs to a table, displays the table name:

    $p = $context->get_paragraph(content => "xyz");
    die "Content not found\n" unless $p;
    $t = $p->get_parent_table;
    say $t ? $t->get_name : "Not in a table";

Table content retrieval ^

A table object provides methods that allow to retrieve any column, row or cell using its logical position. A position may be expressed using either zero-based numeric coordinates, or alphanumeric, spreadsheet-like coordinates. For example the top left cell should be addressed either by (0,0) or by "A1". On the other hand, numeric coordinates only allow the user to address an object relatively to the end of the table; for example, (-1,-1) designates the last cell of the last row whatever the table size.

Table object selection methods return a null value, without error, when the given address is out of range.

The number of rows and columns may be got using the odf_table get_size method.

An individual cell is selected using get_cell with either a pair of numeric arguments corresponding to the row then the column, or an alphanumeric argument whose first character is a letter. The second argument, if provided, is ignored as soon as the first one begins with a letter.

The two following instructions are equivalent and return the second cell of the second row in a table (assuming that $t is a previously selected table):

        $cell = $t->get_cell('B2');
        $cell = $t->get_cell(1, 1);

get_row() allows the user to select a table row as an ODF element. This method requires a zero-based numeric value.

get_column() works according to the same logic and returns a table column ODF element.

The full set of row and column objects may be selected using the table-based get_rows() and get_columns() methods. By default these methods return respectively the full list of rows or columns. They can be restricted to a specified range of rows or columns. The restriction may be expressed through two numeric, zero-based arguments indicating the positions of the first and the last item of the range. Alternatively, the range may be specified using a more "spreadsheet-like" syntax, in only one alphanumeric argument representing the visible representation of the range through a GUI; this argument is the concatenation of the visible numbers of the starting and ending elements, separated by a ":", knowing that "1" is the visible number of the row zero while "A" is the visible number or the column zero. As a consequence, the two following instructions are equivalent and return a list including the rows from 5 to 10 belonging to the table t:

        @rows = $t->get_rows(5, 10);
        @rows = $t->get_rows('6:11');

According to the same logic, each of the two instruction below returns the columns from 8 to 15:

        @cols = $t->get_columns(8, 15);
        @cols = $t->get_columns('I:P');

Once selected, knowing that cells are contained in rows, a row-based get_cell() method is provided. When called from a row object, get_cell() requires the same parameter as the table-based get_column() method. For example, the following sequence returns the same cell as in the previous example:

        $r = $t->get_row(1);
        $c = $r->get_cell(1);

A column-based get_cell() method is provided, too, but it's much less efficient. In addition, the column-based get_cell() may fail with a warning when used in read optimize mode (see below).

A row set may be selected according to the content of a specified column, thanks to get_rows_by_index(). The following example selects all the rows (if any) where the 'C' cell (i.e. the cell at the 3rd position) contains "XYZ":

        @rows = $table->get_rows_by_index(C => "XYZ");

Note that this method allows an alternative syntax; the column may be specified by its numeric (zero-based) position:

        @rows = $table->get_rows_by_index(2, "XYZ");

The first argument (or the key in hash notation) specifies the "index" (i.e. the column that must match a given condition) while the second argument is the search value. The result set is selected according to a smart match.

Alternatively, get_row_by_index() returns the first matching row, like get_rows_by_index() in scalar context.

Remember that there is no real index in a spreadsheet table; this method mimics the use of an arbitrary column as the "key" to select a data set, but the underlying mechanism is not a database engine; the rows are scanned sequentially, so take care of possible performance issues with large tables.

Cell range selection ^

get_cells extracts rectangular ranges of cells in order to allow the applications to store and process them out of the document tree, through regular 2D tables. The range selection is defined by the coordinates of the top left and the bottom right cells of the target area. get_cells allows two possible syntaxes, i.e. the spreadsheet-like one and the numeric one. The first one requires an alphanumeric argument whose first character is a letter and which includes a ':', while the second one requires four numeric arguments. As an example, the two following instructions, which are equivalent, return a bi-dimensional array corresponding to the cells of the B2:D15 area of a table:

        @cells = $table->get_cells("B2:D15");
        @cells = $table->get_cells(1,1,14,3);

Note that, after such a selection, $cells[0][0] contains the "B2" cell of the ODF table.

If get_cells is called without argument, the selection covers the whole table.

A row object has its own get_cell() method. The row based version of get_cells() returns, of course, a one-row table of cell objects. When used without argument, it selects all the cells of the row. It may be called with either a pair of numeric arguments that represent the start and the end positions of the cell range, or an alphanumeric argument (whose the numeric content is ignored and should be omitted) corresponding to the start and end columns in conventional spreadsheet notation. The following example shows two ways to select the same cell range (beginning at the 2nd position and ending at the 26th one) in a previously selected row:

        @cells = $r->get_cells('B:Z');
        @cells = $r->get_cells(1, 25);

The elements of the Perl table returned by get_cells are references to the cells of the ODF table (not copies); the Perl table just maps an ODF table area, and any cell property change made through this Perl table affects the underlying ODF cell.

A column-based version of get_cells() is available, too, but it should be avoided with large tables, and it may explicitly fail in read optimize mode.

Named cell ranges ^

A spreadsheet may contain cell ranges identified by persistent names. lpOD allows the user to retrieve or create such named ranges in some situations.

While it appears in a given table, a named range is not a table element; it's defined at the document level, so it's selected or inserted through document- based methods.

An existing named range may be selected using get_named_range() from the document. The name of the range is the only one required argument:

        my $range = $doc->get_named_range("MyRange");

The returned object is an ODF::lpOD::NamedRange, whose description may be got through get_properties(), that returns a hash (in array context) or a hash ref (in scalar context) that contains the following items:

The ODF::lpOD::NamedRange class provides a get_cells() method, that returns the same results as the table-based get_cells(), but that doesn't require any argument. So, the two following sequences produce the same final result:

        # first form
        $p = $doc->get_named_range("RangeName");
        $table = $doc->get_body->get_table($p->{table});
        @cells = $table->get_cells($p->{range});

        # second form
        @cells = $doc->get_named_range("RangeName")->get_cells;

A get_cell_values() method is provided, too. It produces the same result as the table-based get_cell_values() method, but, of course, it requires only one argument (the data type). Example:

        $r = $doc->get_named_range("RangeName")->get_cell_values('float');
        say "I found $r->[0] float values in the range";
        say "...the min is $r->[1] and the max is $r->[2]";
        say "...and the grand total is $r->[3]";

The possible uses of get_cell_values() are documented in the section dedicated to special cell value extractors in the present manual chapter.

The document-based set_named_range() method allows the applications to create new named ranges. It requires a unique range name as its first argument. The other parameters must be provides according to the same principles as the return value of get_properties(), introduced above. As an example, the following instruction registers a new range running from "C4" to "F12", whose name is "MyArea" in the "Sheet1" table:

        $doc->set_named_range(
                "MyArea",
                table   => "Sheet1",
                range   => "C4:F12"
        );

The example below creates a named range whose properties are borrowed from an existing named range belonging to another document:

        my $range_spec = $doc1->get_named_range("R1")->get_properties;
        $doc2->set_named_range("R1", $range_spec);

The 'usage' parameter is optional; it's default value is 'none'.

The return value of set_named_range() is the new named range object.

The properties of an existing named range may be changed at any time using set_properties().

Be careful: while the uniqueness of the name is checked by set_named_range() there is no other consistency check. So the user is allowed to register a named range without table or range specification, or with a non existent table name, or with a range where the starting cell comes after the ending one.

A named range, once retrieved, may be removed using the standard delete() element-based method. Example:

        $nr = $doc->get_named_range("MyRange");
        $nr && $nr->delete;

Note that get_named_range() and set_named_range() work in spreadsheet documents only.

Row and column customization ^

The objects returned by get_row and get_column can be customized using the standard set_attribute or set_attributes method. Possible attributes are:

The style may be get or set using get_style or set_style.

Table expansion and shrinking ^

Row and column insertion

A table may be expanded vertically and horizontally, using its add_row and add_column methods.

add_row allows the user to insert one or more rows at a given position in the table. The new rows are copies of an existing one. Without argument, a single row is just appended as the end. A number named parameter specifies the number of rows to insert.

An optional before named parameter may be provided; if defined, the value of this parameter must be a row number (in numeric, zero-based form) in the range of the table; the new rows are created as clones of the row existing at the given position then inserted at this position, i.e. before the original reference row. A after parameter may be provided instead of before; it produces a similar result, but the new rows are inserted after the reference row. Note that the two following instructions produce the same result (assuming $t is a previously selected or created table):

        $t->add_row(number => 1, after => -1);
        $t->add_row();

The instruction below creates new rows at the beginning of the table:

        $t->add_row(number => 4, before => 0);

The inserted rows are initialized as clones of the row used as the reference through the after or before or of the last existing row if the new row in appended at the end. So the new rows (and their cells) inherit the same style and content as an existing one.

However, a few options allow the applications to override this default behavior:

The add_column method does the same thing with columns as add_row for rows, and allows the same options. However, because the cells belong to rows, it works according to a very different logic. add_column inserts new column objects (clones of an existing column), then it goes through all the rows and inserts new cells (cloning the cell located at the reference position) in each one.

Of course, it's possible to use insert_element in order to insert a row, a column or a cell externally created (or copied from an other table from another document), provided that the user carefully checks the consistency of the resulting construct. As an example, the following sequence appends a copy of the first row of $t1 after the 5th row of $t2:

   $to_be_inserted = $t1->get_row(0)->clone;
   $t2->insert_element($to_be_inserted, after => $t2->get_row(5));

While a table may be expanded vertically using add_row, each row may be expanded using the odf_row add_cell method whose parameters and behavior are the same as the table-based add_row method.

Row and column deletion

Rows and columns may be individually deleted using delete_row() and delete_column(), respectively. The required argument for these methods is the row or column position in the table, i.e. the same as get_row() or get_column().

The common delete() method may be used from a previously selected row or column object. So, the two snippets below are equivalent:

        # with delete_row
        $table->delete_row($row_number);

        # without delete_row
        $row = $table->get_row($row_number);
        $row->delete;

Knowing that table cells are contained in row, removing a row automatically removes the corresponding cells. The internal logic of delete_column(), that removes the cells of the deleted column, behaves as if the cells were contained in the columns, too. However, it's possible to delete a column without deleting the corresponding cells. To do so, a propagate option must be provided and set to FALSE. Such option may put the table in an inconsistent state, so it should be used for very special purposes only (such as cleaning an inconsistent table).

The delete() method should not be confused with the clear() method that, when called from a row or column object, removes the content of every cell in the row or column but doesn't remove any cell, row or column.

Row and column group handling ^

The content expansion and content selection methods above work with the table body. However it's possible to manage groups of rows or columns. A group may be created with existing adjacent rows or columns, using set_row_group() and set_column_group() respectively. These methods take two arguments, which are the numeric positions of the starting and ending elements of the group. However, these numeric arguments may be replaced by a single alphanumeric range definition argument, so the following instructions are equivalent; both create a group including the same 3 columns ("C" to "E"):

        $column_group = $table->set_column_group(3, 5);
        $column_group = $table->set_column_group("C:E");

The same idea apply to row groups; however, beware that in range alphanumeric notation, the numbers represents the spreadsheet end-user point of view, so they are one-based; as an example, the two following instructions, that create a row group including the rows 3 to 5, are equivalent:

        $row_group = $table->set_row_group(3, 5);
        $row_group = $table->set_row_group("4:6");

In addition, an optional display named boolean parameter may be provided (default=TRUE), instructing the applications about the visibility of the group.

Both set_row_group() and set_column_group() return an object which can be used later as a context object for any row, column or cell retrieval or processing. An existing group may be retrieved according to its numeric position using get_row_group() or get_column_group() with the position as argument, or without argument to get the first (or the only one) group.

A group can't bring a particular style; it's just visible or not. Once created, its visibility may be turned on and off by changing its display value through set_attribute().

Knowing that cells depends on rows, a row group provides the same get_cell() method as a table. It provides a get_row() method, while a column group provides a get_column() one.

A row group provides a add_row() method, while a column group provides a add_column() method. These methods work like their table-based versions, and they allow the user to expand the content of a particular group.

Row and column group may be collapsed or expanded using their collapse() and uncollapse() methods.

It's possible to delete all the cell contents of a group using clear(). This method doesn't remove any row or column; it just erases the content and, if any, the style and the annotation of every cell. Beware that the column group based version of clear() is much slower than the row group based version.

Table headers ^

One or more rows or columns in the beginning of a table may be organized as a header. Row and columns headers are created using the set_row_header() and set_column_header() table-based methods, and retrieved using get_row_header() and get_column_header(). A row header object brings its own add_row() method, which works like the table-based add_row() but appends the new rows in the space of the row header. The same logic applies to column headers which have a add_column() method. An optional positive integer argument may specify the number or rows or columns to include in the header (default=1).

Note that a column header is a row or a set of rows containing column titles that should be automatically repeated on every page if the table does not fit on a single page, while a row headers is a column or a set of columns containing row titles. In the present version, row headers are not fully supported.

A table can't directly contain more than one row header and one column header. However, a column group can contain a column header, while a row group can contain a row header. So the header-focused methods above work with groups as well as with tables.

A table header doesn't bring particular properties; it's just a construct allowing the author to designate rows and columns that should be automatically repeated on every page if the table doesn't fit on a single page.

The ``get_xxx()`` table-based retrieval methods ignore the content of the headers. However, it's always possible to select a header, then to used it as the context object to select an object using its coordinates inside the header. For example, the first instruction below gets the first cell of a table body, while the third and third instructions select the first cell of a table header::

   c1 = table.get_cell(0,0)
   header = table.get_header()
   c2 = header.get_cell(0,0)

Individual cell property handling ^

A cell owns both a content and some properties which may be processed separately.

The cell content is a list of one or more ODF elements. While this content is generally made of a single paragraph, it may contain several paragraphs and various other objects. The user can attach any content element to a cell using the standard insert_element method. However, for the simplest (and the most usual) cases, it's possible to use set_text. The cell-based set_text method diffs from the generic odf_element set_text: it removes the previous content elements, if any, then creates a single paragraph with the given text as the new content. In addition, this method accepts an optional style named parameter, allowing the user to set a paragraph style for the new content. To insert more content (i.e. additional paragraphs and/or other ODF elements), the needed objects have to be created externally and attached to the cell using insert_element or append_element. Alternatively, it's possible to remove the existing content (if any) and attach a full set of content elements in a single instruction using set_content; this last cell method takes a list of arbitrary ODF elements and appends them (in the given order) as the new content.

The generic group() method may be used to grab a list of paragraphs in order to move them in the cell. As an example, the following instruction moves all the paragraphs containing a given substring in a given cell:

    $table->get_cell("B4")->group(
        $doc->get_body->get_paragraphs(content => "XYZ")
        );

The get_content cell method returns all the content elements as a list. For the simplest cases, the cell-based get_text method directly returns the text content as a flat string, without any structural information and whatever the number and the type of the content elements.

The cell properties may be read or changes using get_xxx and set_xxx methods, where xxx stands for one of the following:

If set_currency is used with a non-null value, then the type of the cell is automatically set to 'currency'. If set_type forces a type that is not 'currency', then the cell currency is unset.

A cell may be annotated using set_annotation(). The cell-based version of this method works like the paragraph-based version, described in ODF::lpOD::TextElement, but the positioning options are ignored. A cell annotation is not linked to a text position and may be attached to an empty cell. A display boolean option (whose default is FALSE) may be provided in order to make the annotation automatically visible in the sheet.

It's possible to remove all the content and the properties of a cell but its style, including any possible formula, annotation, and so on, with the clear() method. In addition, clear() removes any multi-row or multi- column span.

Note that it's possible to clear the content of all the cells of a row, a column, a row group, a column group, or a table, with the respective clear() methods of these objects. These methods don't remove the cells themselves. However, remember that the column and column group based versions of clear() are very slow.

The cell coordinates may be retrieved using get_position(). In scalar context, this method returns the local position in the row. In array context, it returns the table name, the row number and the column number. In addition, get_parent_table() returns the table object itself, while get_parent_row() returns the including row.

Special cell value extractors ^

A few access methods are available to directly get the value(s) of one ore more specified cells, without explicit access to the cell objects. These accessors are not syntactic sugar only; they may allow better performances in some situations.

Individual cell value extraction

An application may directly get the value of a specified cell without previous selection of the cell object. As an example, the two following instructions produce the same result:

        $value = $table->get_cell($row, $column)->get_value;
        $value = $table->get_cell_value($row, $column);

Data set extraction or aggregate computation

Alongside the get_cells() method, a get_cell_values() method allows the user to get either value lists or basic value aggregates. This method requires a regular cell data type as its first argument, followed by a cell range specification according to the same logic as get_cells(). The cells whose data type is not the given type are ignored. As an example, the following example creates a value list whose content comes from all the currency cells of the "E2:G10" range:

        @values = $table->get_cell_values('currency', 'E2:G10');

The allowed types are string, date, time, float, currency, and boolean. However, a special all indicator may be used as first argument instead of a regular data type; if so, all the non-empty cells are selected.

In the resulting 2D list, undef values occupy the places of non-matching or empty cells, in order to provide a consistent mapping of the corresponding table area.

get_cell_values() may be used as a row or column method. The most efficient one is the row-based version. Both return a one-dimension list, without null value (the non-matching and empty cells are ignored). So the instruction below produces a list of all the currency amounts found between (and including) the 3rd and the 8th cells of the 4th row of a table:

        $row = $table->get_row(3);
        @amounts = $row->get_cell_values('currency', 'C:H');

get_cell_values(), when used in scalar context, returns a small array ref whose item 0 is the number of non-empty cells matching the given type in the range, and whose the following items depend on the data type. The two following positions are the min and the max values for every type but boolean; for booleans, they respectively contain the number of true values and the number of false values. For the string type, the min and the max are selected by default according to the standard Perl cmp string comparison function (that is not always convenient for international character sets), but the user may provide a custom function (whose external behavior must comply with cmp, i.e. whose possible results are -1, 0, 1). An additional item, containing the arithmetic sum, is provided at the last position for the float, currency and percentage types only. As an example, the following code displays the count, the min, the max and the sum of the float cells in the "E2:G10" range:

        $r = $table->get_cell_values('float', 'E2:G10');
        say "I found $r->[0] values";
        say "...from $r->[1] to $r->[2]";
        say "...and the grand total is $r->[3]";

Flat text export

A special get_text() method is provided with tables or row groups. Knowing that a table shouldn't directly contain text (the text content, if any, belong to cells), this method returns the concatenated contents of all the cells as a flat string. It's useful only to allow the applications to quickly check if at least one cell contains something, or if a particular substring is present somewhere in the table. Note that the returned text doesn't always reflect the visible content of the cells: for non-string cells, the exported content is the value, not its formatted representation.

Cell span expansion ^

A cell may be expanded so it covers one or more adjacent columns and/or rows. The cell-based set_span() method allows the user to control this expansion. It takes rows and columns as parameters, specifying the number of rows and the number of columns covered. The following example selects the "B4" cell then expands it over 4 columns and 3 rows:

        $cell = $table->get_cell('B4');
        $cell->set_span(rows => 3, columns => 4);

The existing span of a cell may be get using get_span(), which returns the rows and columns values.

This method changes the previous span of the cell. The default value for each parameter is 1, so a set_span() without argument reduces the cell at its minimal span.

When a cell is covered due to the span of another cell, it remains present and holds its content and properties. However, it's possible to know at any time if a given cell is covered or not through the boolean is_covered() cell method. In addition, the span values of a covered cell are automatically set to 1, and set_span() is forbidden with covered cells.

Note that a cell that spreads over multiple rows and/or columns is reduced to the minimal size by clear().

Performance issues ^

The table-oriented access methods perform relatively well against tables including up to thousands, if not tens of thousands of cells. So there is no performance issue with tables belonging to text documents. On the other hand, spreadsheet documents may contain tables whose size in potentially unlimited. As soon as you are faced to wrong response times and overloaded CPUs, you may consider using the following workarounds, which can (sometimes) improve the performances, possibly at the cost of a reduced functionality.

New table creation

Each time a new empty table is created through odf_create_table() or odf_table-create()>, a expand optional boolean parameter, whose default value is FALSE, is available. This parameter controls the way the table is internally stored.

If it's set to TRUE, the table is stored in expanded mode. It's a good choice for small tables or for large tables where cells spread over the largest part of its area will be populated by the application. On the other hand, large spreadsheet tables whose content will remain mostly empty (or filled with repetitive values and styles) should not be expanded at the creation time.

The expand option should generally not be changed for spreadsheets. However, the user should set it to TRUE for tables included in presentation documents, because some ODF-compliant office products (such as LibreOffice Impress) apparently can't properly render tables stored in compact form.

While the effect of this option is almost unnoticeable with small tables, the full storage expansion of a mid-sized or large table (i.e. thousands of cells) may have a significant impact on processing time and memory consumption.

Accessing cells from rows

Remember that cells belong to rows and rows belong to tables. As a consequence, accessing a cell is faster from the row than from the table. So, each time you need to get several cells belonging to the same row, you should first get the row then use it as the context for subsequent cell accesses. As an illustration, each of the two following code snippets scans a whole table and loads the text of every cell in a list, but the second one is faster:

        # table scan, way 1
        my @text = ();
        my ($l, $w) = $table->get_size;
        for (my $i = 0 ; $i < $l ; $i++) {
                for (my $j = 0 ; $j < $w ; $j++) {
                        push @text, $table->get_cell($i, $j)->get_text;
                        }
                }

        # table scan, way 2
        my @text = ();
        my ($l, $w) = $table->get_size;
        for (my $i = 0 ; $i < $l ; $i++) {
                my $row = $table->get_row($i);
                for (my $j = 0 ; $j < $w ; $j++) {
                        push @text, $row->get_cell($j)->get_text;
                        }
                }

At a higher level but for the same reasons, get_cell() and get_cells() are slower as column group methods that as table or row group methods. In other words, when a cell belongs to the intersection of a row group and a column group, it may be accessed faster from the table or the row group than from the column group.

Selecting cell values instead of cells

Each time an application needs to get cells in order to extract their values without update, the special get_cell_value() and get_cell_values() methods should be preferred.

As an example, the two following instructions produce the same result but the second one is more efficient in a large table:

        $value = $table->get_cell($row, $column)->get_value;
        $value = $table->get_cell_value($row, $column);

Similarly, the two following snippets produce the same result set but the second one is more efficient (and not only code-saving) than the first one in a large spreadsheet:

        # first form
        @values = ();
        push @values, scalar $_->get_value
                for $row->get_cells($start, $end);

        # second form
        @values = $row->get_cell_values($start, $end);

Mapping ODF tables with Perl lists

Thanks to get_cells(), you can easily associate a Perl table to a selected area in a document table. As an example, the following instruction produces a 2D Perl list that maps the "B4:Z50" area in a given table:

        my @cells = $table->get_cells("B4:Z50");

While get_cells() is a costly method, it provides an array of pre-selected cells. Beware that get_cells() returns the cells themselves, not copies, so, after the instruction above, $cells[0][0] is the "B4" cell of the ODF table, while $cells[-1][-1] is the "Z50" cell, and so on. As a consequence, the 2 instructions below are functionally equivalent, but the second one in much faster because there is no need to look for the cell in the XML data structure:

        $text = $table->get_cell("C5")->get_text;
        $text = $cells[1][1]->get_text;

Using such a mapping doesn't significantly improve the overall performances, but it allows the applications to execute the slow job once for all, then provide a good interactivity. However, be careful about very large areas: using get_cells() to load hundreds of thousands of cells is too slow to be practical. In addition, the mapping is no longer accurate as soon as the structure of the underlying table is changed due to row/column insertions or deletions. For read-only access, have a look at the "read optimized" option (introduced below) that could help.

Working area limitation

The global size of a typical spreadsheet table is by far larger than the size of the really used part. As an example, your spreadsheet processor may silently store a 65536x1024 table while the last really used cell is, say, Z50, so the size of the useful part is 50x26. In such a situation, lpOD can't automatically decide what is the useful size, so it processes the full size. The first result is a huge time and resource waste. As soon as you know the useful size of a table, you can instruct the odf_table instance to ignore the extra area, thanks to set_working_area(). The instruction below tells that, for the current session, the table will be processed as if its size was 500x100:

        my $table = $doc->get_body->get_table("Sheet1");
        $table->set_working_area(500, 100);

Note that this operational restriction has no effect if the real size is smaller than the given size. On the other hand, set_working_area() doesn't destroy the table content that resides out of the working area, if any; it just prevents you from accessing any object beyond your declared limits through the official table-oriented methods, namely get_row(), get_cell(), and get_column(). However, the "hidden" area remains available for low-level hacking with basic element handling methods (for example, if you issue a get_paragraphs() from the table object, it will look for all the paragraphs belonging to all the real cells of the calling table).

The working area restriction doesn't produce any persistent effect when the document is saved.

Note that the get_size() method itself is affected by set_working_area(); it returns the declared size, unless the real size is smaller.

You can change the working area according to your current needs. Successive calls of set_working_area() are allowed, so the working area may be enlarged or reduced at will.

The working area restriction may be removed using set_working_area() without argument.

Read-optimization

As soon as an object is selected using any official table component selector (such as get_cell(), get_row(), and so on), lpOD acts by default as if this object could be updated or deleted, and as if something (a row, a column or a cell) could be inserted before or after it. As a consequence, the internal data structure of the spreadsheet may be changed, resulting in useless processing if case of read-only access. However, lpOD allows the applications to use tables in "read optimized" mode, so it may avoid any update preparation, allowing better response times. To activate this mode, the user must set the "read optimized" flag to TRUE using read_optimize() like that:

        my $table = $doc->get_body->get_table("Sheet1");
        $table->read_optimize(TRUE);

Caution: read_optimize() means that you assume that you will not make updates; it doesn't prevent you from updating cells, deleting rows, and so on. So, be careful: you can corrupt the table and get very strange and unpredictable results as soon as you make updates in read optimized mode.

This optimization option is useful for large table area scans, particularly with very sparse tables (i.e. tables where significant cells are separated by large empty areas). On the other hand, it's not efficient, and at worst may increase the response time, for individual access to a cell. In addition, it's completely useless with small tables as well as with dense tables (i.e. tables without large empty areas and without large sequences of identical objects). So don't use it without testing. In some cases, the read-optimize mode inhibits the column-based cell retrieval methods, while it may improve the response times of table- and row-based retrieval methods.

Note that you can switch this mode off and restore the default behavior at any time. You just have to recall read_optimize() with FALSE as argument. Like set_working_area(), read_optimize() doesn't produce any persistent effect.

However, there is a possible trap, illustrated by the next (wrong) example:

        $table->read_optimize(TRUE);
        $cell = $table->get_cell("Z26");
        $table->read_optimize(FALSE);
        $cell->set_value(1234);

In this sequence, we selected a cell while the table was in "read optimized" mode, then we canceled this mode and executed an update. The result is not predictable (it will be sometimes right, sometimes wrong). The general principle is: avoid updating an object selected in read optimized mode. However, there is an important exception: a cell that was selected in read- optimized mode may be safely updated if (and only if) its differs from the two neighbour cells and if it's belong to a row that differs (by at least one cell) from the two neighbour rows. These conditions are almost always met with tables whose one of the columns contains identifiers and each of the other columns displays data of various types and formats.

On the other hand, the read optimize flag is useless with methods that return values and not objects (i.e. get_cell_value, get_cell_values).

Compacting empty areas

Cells, rows, row groups, tables, columns and column groups own a clear() method. When the calling context is a table, a row, or a row group, a compact boolean option, whose default is FALSE, is allowed. If this option is set to TRUE, the execution of clear() is faster and the physical storage of the processed cells is compacted.

This option is recommended in spreadsheet documents only.

Caution: the benefits of the compact option are not effective if the cleared area is immediately used as the target of a lot of individual cell accesses using get_cell(), knowing that in such case lpOD will have to un-compact a lot of cells in the area. As a consequence, this option is not recommended when clear() is used to prepare a massive table update.

AUTHOR/COPYRIGHT ^

Developer/Maintainer: Jean-Marie Gouarne http://jean.marie.gouarne.online.fr Contact: jmgdoc@cpan.org

Copyright (c) 2010 Ars Aperta, Itaapy, Pierlis, Talend. Copyright (c) 2011 Jean-Marie Gouarne.

This work was sponsored by the Agence Nationale de la Recherche (http://www.agence-nationale-recherche.fr).

License: GPL v3, Apache v2.0 (see LICENSE).

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