Patrick Donelan > PSPP-Perl-0.7.2.20090730 > Examples.pod

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PSPP::Examples ^

This page shows some simple examples of using the PSPP module. See PSPP for details on each of the subroutines.

A Simple example

This example creates a system file called foo.sav, containing one variable called "id". It contains no data.

        use PSPP;

        my $dict = PSPP::Dict->new ();
        my $var = PSPP::Var->new ($dict, "id");

        my $sysfile = PSPP::Sysfile->new ("foo.sav", $dict);
        $sysfile->close();

A slightly more complex example

In this example there are three variables, called "id", "name" and "dob". Their formats are F2.0, A80 and DATETIME17 respectively.

        use PSPP;

        my $dict = PSPP::Dict->new ();
        PSPP::Var->new ($dict, "id",
                   (fmt=>PSPP::Fmt::F, width=>2, decimals=>0) );
        
        PSPP::Var->new ($dict, "name", (fmt=>PSPP::Fmt::A, width=>80) );
        PSPP::Var->new ($dict, "dob",  (fmt=>PSPP::Fmt::DATETIME) );

        my $sysfile = PSPP::Sysfile->new ("foo.sav", $dict);
        $sysfile->close();

Changing the properties of variables

After a variable has been created, parameters may be set for it.

        use PSPP;

        my $dict = PSPP::Dict->new ();
        my $var1 = PSPP::Var->new ($dict, "id");

        $var1->set_label ("A unique identifier");
        $var1->add_value_label (0, "Zero");
        $var1->add_value_label (1, "One");

Appending data to the file

When a file is created, it contains no data. Data is added by appending cases to the file.

This example creates a file with 3 cases.

        use PSPP;

        my $dict = PSPP::Dict->new ();
        PSPP::Var->new ($dict, "id", 
           (fmt=>PSPP::Fmt::F, width=>2, decimals=>0) );

        PSPP::Var->new ($dict, "name", (fmt=>PSPP::Fmt::A, width=>8) );

        my $sysfile = PSPP::Sysfile->new ("foo.sav", $dict);

        $sysfile->append_case ( [1, "Alf"] );
        $sysfile->append_case ( [2, "Bert"] );
        $sysfile->append_case ( [3, "Charlie"] );

        $sysfile->close();

Variables with differing input and output formats

By default, a variable's output format corresponds to the input format. However, the output format may be changed after the variable has been created.

This example shows how to create a DATETIME variable using the current time as its value. Since pspp uses a different epoch to perl, the constant PSPP::PERL_EPOCH needs to be added to the value returned from time(), in order that it be correctly represented by pspp.

        use PSPP;

        my $dict = PSPP::Dict->new ();

        my $var1 = PSPP::Var->new ($dict, "entrytime", 
                (fmt=>PSPP::Fmt::F) );

        $var1->set_output_format ( (fmt=>PSPP::Fmt::DATETIME, width=>20) );

        my $sysfile = PSPP::Sysfile->new ("foo.sav", $dict);

        my $now = time ();

        $sysfile->append_case ( [ $now  + PSPP::PERL_EPOCH]  ) 
                || die "Cant write case";
        
        $sysfile->close();

Reading data

Data can be read from a system file or other source:

        use PSPP;

        my $sf = PSPP::Reader->open ("foo.sav");

        my $dict = $sf->get_dict ();

Once opened, the dictionary can be used like any other.

        for ($v = 0 ; $v < $dict->get_var_cnt() ; $v++)
        {
            my $var = $dict->get_var ($v);

            # Print the variables
            my $name = $var->get_name ();
            my $label = $var->get_label ();
            print "Var: $name, Label: $label\n";

            # Retrieve and print the value labels
            my $vl = $var->get_value_labels ();
            print "$_: $vl->{$_}\n" for keys %$vl;
        }

Reading of data must be done sequentially using the get_next_case method.

        while (my $c = $sf->get_next_case () )
        {
            my $v;
            for ($v = 0; $v < $dict->get_var_cnt(); $v++)
            {
                print "val$v: @$c[$v] ";
            }
            print "\n";
        }
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