Darren Duncan > Data-MultiValuedHash-1.081 > Data::MultiValuedHash

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Module Version: 1.081   Source  

NAME ^

Data::MultiValuedHash - Hash whose keys have multiple ordered values

DEPENDENCIES ^

Perl Version

        5.004

Standard Modules

        I<none>

Nonstandard Modules

        I<none>

SYNOPSIS ^

        use Data::MultiValuedHash;

        $mvh = Data::MultiValuedHash->new();  # make empty, case-sensitive (norm)
        $mvh = Data::MultiValuedHash->new( 1 );  # make empty, case-insensitive
        $mvh = Data::MultiValuedHash->new( 0, {
                name => 'John',
                age => 17,
                color => 'green',
                siblings => ['Laura', 'Andrew', 'Julia'],
                pets => ['Cat', 'Bird'],
        } );  # make new with initial values, case-sensitive keys

        $mvh->store( age => 18 );  # celebrate a birthday

        $mvh->push( siblings => 'Tandy' );  # add a family member, returns 4

        $mvh->unshift( pets => ['Dog', 'Hamster'] );  # more pets

        $does_it = $mvh->exists( 'color' );  # returns true

        $name = $mvh->fetch_value( 'siblings' );  # returns 'Laura'
        $name = $mvh->fetch_value( 'siblings', 2 );  # returns 'Julia'
        $name = $mvh->fetch_value( 'siblings', -1 );  # returns 'Tandy'
        $rname = $mvh->fetch( 'siblings' );  # returns all 4 in array ref
        @names = $mvh->fetch( 'siblings' );  # returns all 4 as list

        $name = $mvh->fetch_value( 'Siblings' );  # returns nothing, wrong case
        $mv2 = Data::MultiValuedHash->new( 1, $mvh );  # conv to case inse
        $name = $mv2->fetch_value( 'Siblings' );  # returns 'Laura' this time
        $is_it = $mvh->ignores_case();  # returns false; like normal hashes
        $is_it = $mv2->ignores_case();  # returns true

        $color = $mvh->shift( 'color' );  # returns 'green'; none remain

        $animal = $mvh->pop( 'pets' );  # returns 'Bird'; three remain

        %list = $mvh->fetch_all();  # want all keys, all values
                # returns ( name => ['John'], age => [18], color => [], 
                # siblings => ['Laura', 'Andrew', 'Julia', 'Tandy'], 
                # pets => ['Dog', 'Hamster', 'Cat'] )

        %list = $mvh->fetch_first();  # want all keys, first values of each
                # returns ( name => 'John', age => 18, color => undef, 
                # siblings => 'Laura', pets => 'Dog' )

        %list = $mvh->fetch_last();  # want all keys, last values of each
                # returns ( name => 'John', age => 18, color => undef, 
                # siblings => 'Tandy', pets => 'Cat' )

        %list = $mvh->fetch_last( ['name', 'siblings'] );  # want named keys only
                # returns ( name => 'John', siblings => 'Tandy' )

        %list = $mvh->fetch_last( ['name', 'siblings'], 1 );  # want complement
                # returns ( age => 18, color => undef, pets => 'Cat' )

        $mv3 = $mvh->clone();  # make a duplicate of myself
        $mv4 = $mvh->fetch_mvh( 'pets', 1 );  # leave out the pets in this "clone"

        @list = $mv3->keys();
                # returns ('name','age','color','siblings','pets')
        $num = $mv3->keys();  # whoops, doesn't do what we expect; returns array ref
        $num = $mv3->keys_count();  # returns 5

        @list = $mv3->values();
                # returns ( 'John', 18, 'Laura', 'Andrew', 'Julia', 'Tandy', 
                # 'Dog', 'Hamster', 'Cat' )
        @num = $mv3->values_count();  # returns 9

        @list = $mvh->splice( 'Siblings', 2, 1, ['James'] );
        # replaces 'Julia' with 'James'; returns ( 'Julia' )

        $mv3->store_all( {
                songs => ['this', 'that', 'and the other'],
                pets => 'Fish',
        } );  # adds key 'songs' with values, replaces list of pets with 'fish'

        $mv3->store_value( 'pets', 'turtle' );  # replaces 'fish' with 'turtle'
        $mv3->store_value( 'pets', 'rabbit', 1 );  # pets is now ['turtle','rabbit']

        $oldval = $mv3->delete( 'color' );  # gets rid of color for good
        $rdump = $mv3->delete_all();  # return everything as hash of arrays, clear

DESCRIPTION ^

This Perl 5 object class implements a simple data structure that is similar to a hash except that each key can have several values instead of just one. There are many places that such a structure is useful, such as database records whose fields may be multi-valued, or when parsing results of an html form that contains several fields with the same name. This class can export a wide variety of key/value subsets of its data when only some keys are needed.

While you could do tasks similar to this class by making your own hash with array refs for values, you will need to repeat some messy-looking code everywhere you need to use that data, creating a lot of redundant access or parsing code and increasing the risk of introducing errors.

One optional feature that this class provides is case-insensitive keys. Case-insensitivity simplifies matching form field names whose case may have been changed by the web browser while in transit (I have seen it happen).

SYNTAX ^

This class does not export any functions or methods, so you need to call them using object notation. This means using Class->function() for functions and $object->method() for methods. If you are inheriting this class for your own modules, then that often means something like $self->method().

All method arguments and results are passed by value (where appropriate) such that subsequent editing of them will not change values internal to the MVH object; this is the generally accepted behaviour.

Most methods take either KEY or VALUES arguments. KEYs are always treated as scalars and VALUES are taken as a list. Value lists can be passed either as an ARRAY ref, whereupon they are internally flattened, or as an ordinary LIST. If the first VALUES argument is an ARRAY ref, it is interpreted as being the entire list and subsequent arguments are ignored. If you want to store an actual ARRAY ref as a value, make sure to put it inside another ARRAY ref first, or it will be flattened.

Any method which returns a list will check if it is being called in scalar or list context. If the context wants a scalar then the method returns its list in an ARRAY ref; otherwise, the list is returned as a list. This behaviour is the same whether the returned list is an associative list (hash) or an ordinary list (array). Failures are returned as "undef" in scalar context and "()" in list context. Scalar results are returned as themselves, of course.

When case-insensitivity is used, all operations involving hash keys operate with lowercased versions, and these are also what is stored. The default setting of the "ignores case" property is false, like with a normal hash.

FUNCTIONS AND METHODS ^

new([ CASE[, SOURCE] ])

This function creates a new Data::MultiValuedHash (or subclass) object and returns it. All of the method arguments are passed to initialize() as is; please see the POD for that method for an explanation of them.

initialize([ CASE[, SOURCE] ])

This method is used by new() to set the initial properties of objects that it creates. Calling it yourself will empty the internal hash. If you provide arguments to this method then the first one, CASE, will initialize the case-insensitivity attribute, and any subsequent arguments will provide initial keys and values for the internal hash. Nothing is returned.

The first optional argument CASE (boolean) specifies whether this object uses case-insensitive keys; the default value is false.

The second optional argument, SOURCE is used as initial keys and values for this object. If it is a Hash Ref (normal or of arrays), then the store_all( SOURCE ) method is called to handle it. If the same argument is a MVH object, then its keys and values are similarly given to store_all( SOURCE ). Otherwise, SOURCE is ignored and this object starts off empty.

clone([ CLONE ])

This method initializes a new object to have all of the same properties of the current object and returns it. This new object can be provided in the optional argument CLONE (if CLONE is an object of the same class as the current object); otherwise, a brand new object of the current class is used. Only object properties recognized by Data::MultiValuedHash are set in the clone; other properties are not changed.

ignores_case([ VALUE ])

This method is an accessor for the boolean "case insensitive" property of this object, which it returns. If VALUE is defined, this property is set to it.

If the property is being changed from false to true, then any existing keys will be lowercased, and where name collisions occur, the values will be combined. The order of these new values is determined by iterating over the original case-sensitive keys in the order of "sort keys()".

keys()

This method returns a list of all this object's keys.

keys_count()

This method returns a count of this object's keys.

values()

This method returns a flattened list of all this object's values.

values_count()

This method returns a count of all this object's values.

exists( KEY )

This method returns true if KEY is in the hash, although it may not have any values.

count( KEY )

This method returns a count of the values that KEY has. It returns failure if KEY doesn't exist.

fetch_value( KEY[, INDEX] )

This method returns a single value of KEY, which is at INDEX position in the internal array of values; the default INDEX is 0. It returns failure if KEY doesn't exist.

fetch( KEY[, INDEXES] )

This method returns a list of all values that KEY has. It returns failure if KEY doesn't exist. The first optional argument, INDEXES, is an array ref that specifies a subset of all this key's values that we want returned instead of all of them.

fetch_hash([ INDEX[, KEYS[, COMPLEMENT]] ])

This method returns a hash with all this object's keys and a single value of each key, which is at INDEX position in the internal array of values for the key; the default INDEX is 0. The first optional argument, KEYS, is an array ref that specifies a subset of all this object's keys that we want returned. If the second optional boolean argument, COMPLEMENT, is true, then the complement of the keys listed in KEYS is returned instead.

fetch_first([ KEYS[, COMPLEMENT] ])

This method returns a hash with all this object's keys, but only the first value for each key. The first optional argument, KEYS, is an array ref that specifies a subset of all this object's keys that we want returned. If the second optional boolean argument, COMPLEMENT, is true, then the complement of the keys listed in KEYS is returned instead.

fetch_last([ KEYS[, COMPLEMENT] ])

This method returns a hash with all this object's keys, but only the last value for each key. The first optional argument, KEYS, is an array ref that specifies a subset of all this object's keys that we want returned. If the second optional boolean argument, COMPLEMENT, is true, then the complement of the keys listed in KEYS is returned instead.

fetch_all([ KEYS[, COMPLEMENT[, INDEXES]] ])

This method returns a hash with all this object's keys and values. The values for each key are contained in an ARRAY ref. The first optional argument, KEYS, is an array ref that specifies a subset of all this object's keys that we want returned. If the second optional boolean argument, COMPLEMENT, is true, then the complement of the keys listed in KEYS is returned instead. The third optional argument, INDEXES, is an array ref that specifies a subset of all of each key's values that we want returned instead of all of them.

fetch_mvh([ KEYS[, COMPLEMENT[, INDEXES]] ])

This method returns a new MVH object with all or a subset of this object's keys and values. It has the same calling conventions as fetch_all() except that an MVH object is returned instead of a literal hash. The case-insensitivity attribute of the new MVH is the same as the current one.

store_value( KEY, VALUE[, INDEX] )

This method adds a new KEY to this object, if it doesn't already exist. The VALUE replaces any that may have existed before at INDEX position in the internal array of values; the default INDEX is 0. This method returns the new count of values that KEY has, which may be more than one greater than before.

store( KEY, VALUES )

This method adds a new KEY to this object, if it doesn't already exist. The VALUES replace any that may have existed before. This method returns the new count of values that KEY has. The best way to get a key which has no values is to pass an empty ARRAY ref as the VALUES.

store_all( HASH )

This method takes one argument, HASH, which is an associative list or hash ref or MVH object containing new keys and values to store in this object. The value associated with each key can be either scalar or an array. Symantics are the same as for calling store() multiple times, once for each KEY. Existing keys and values with the same names are replaced. New keys are added in the order of "sort CORE::keys %hash". This method returns a count of new keys added.

push( KEY, VALUES )

This method adds a new KEY to this object, if it doesn't already exist. The VALUES are appended to the list of any that existed before. This method returns the new count of values that KEY has.

unshift( KEY, VALUES )

This method adds a new KEY to this object, if it doesn't already exist. The VALUES are prepended to the list of any that existed before. This method returns the new count of values that KEY has.

pop( KEY )

This method removes the last value associated with KEY and returns it. It returns failure if KEY doesn't exist.

shift( KEY )

This method removes the last value associated with KEY and returns it. It returns failure if KEY doesn't exist.

splice( KEY, OFFSET[, LENGTH[, VALUES]] )

This method adds a new KEY to this object, if it doesn't already exist. The values for KEY at index positions designated by OFFSET and LENGTH are removed, and replaced with any VALUES that there may be. This method returns the elements removed from the list of values for KEY, which grows or shrinks as necessary. If LENGTH is omitted, the method returns everything from OFFSET onward.

delete( KEY )

This method removes KEY and returns its values. It returns failure if KEY doesn't previously exist.

delete_all()

This method deletes all this object's keys and values and returns them in a hash. The values for each key are contained in an ARRAY ref.

batch_new( CASE, SOURCE[, *] )

This batch function creates a list of new Data::MultiValuedHash (or subclass) objects and returns them. The symantecs are like calling new() multiple times, except that the argument SOURCE is required. SOURCE is an array and this function creates as many MVH objects as there are elements in SOURCE. The list is returned as an array ref in scalar context and a list in list context. CASE defaults to false if undefined. Any arguments following SOURCE are passed to new() as is.

METHOD RELATIONSHIP OVERVIEW ^

A MultiValuedHash can be seen conceivably as a table where keys are row indices and each value for the key is a column; the columns indices are in value arrays.

When fetching data, we could remove either one cell at a time, or a whole row or a whole column, or a block of cells making parts of a row and or column. This diagram indicates the data type that would be returned by methods corresponding to different fetch types:

              1 v    n v   all v
        1   k scalar array array
        n   k hash   mvh   mvh
        all k hash   mvh   mvh

The following method list indicates the return types of all the standard methods, and how they relate to the conceptual diagram. Pay particular attention to the fetch methods.

        array  = keys()
        scalar = keys_count()
        array  = values()
        scalar = values_count()

        scalar = exists( KEY )

        scalar = count( KEY )

        scalar = fetch_value( KEY[, INDEX] ) - index=0
        array  = fetch( KEY[, INDEXES] ) - indexes=all
        hash   = fetch_hash( INDEX[, KEYS[, COMPLEMENT]] ) - index=0
                hash = fetch_first([ KEYS[, COMPLEMENT] ]) - index=0
                hash = fetch_last([ KEYS[, COMPLEMENT] ])  - index=-1
        mvh    = fetch_all([ KEYS[, COMPLEMENT[, INDEXES ]] ]) - keys=all,ind=all
                mvh = fetch_mvh([ KEYS[, COMPLEMENT[, INDEXES ]] ]) - keys=all,ind=all

        store_value( KEY, VALUE[, INDEX] ) - index=0
        store( KEY, VALUES )
        store_all( HASH )

        push( KEY, VALUES )

        unshift( KEY, VALUES )

        scalar = pop( KEY )

        scalar = shift( KEY )

        array = splice( KEY, OFFSET, LENGTH, VALUES )

        array = delete( KEY )
        mvh   = delete_all()

AUTHOR ^

Copyright (c) 1999-2003, Darren R. Duncan. All rights reserved. This module is free software; you can redistribute it and/or modify it under the same terms as Perl itself. However, I do request that this copyright information and credits remain attached to the file. If you modify this module and redistribute a changed version then please attach a note listing the modifications. This module is available "as-is" and the author can not be held accountable for any problems resulting from its use.

I am always interested in knowing how my work helps others, so if you put this module to use in any of your own products or services then I would appreciate (but not require) it if you send me the website url for said product or service, so I know who you are. Also, if you make non-proprietary changes to the module because it doesn't work the way you need, and you are willing to make these freely available, then please send me a copy so that I can roll desirable changes into the main release.

Address comments, suggestions, and bug reports to perl@DarrenDuncan.net.

CREDITS ^

Thanks to Johan Vromans <jvromans@squirrel.nl> for suggesting the split of my old module "CGI::HashOfArrays" into the two current ones, "Data::MultiValuedHash" and "CGI::MultiValuedHash". This took care of a longstanding logistical problem concerning whether the module was a generic data structure or a tool for encoding/decoding CGI data.

Thanks to Steve Benson <steve.benson@stanford.edu> for suggesting POD improvements in regards to the case-insensitivity feature, so the documentation is easier to understand.

Thanks to Geir Johannessen <geir.johannessen@nextra.com> for alerting me to several "ambiguous call" warnings.

Thanks to Jonathan Snyder <jonathan@mail.method.com> for alerting me to some more "ambiguous call" warnings.

SEE ALSO ^

perl(1), CGI::MultiValuedHash, HTML::FormTemplate, CGI::Portable.

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