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=pod
=for comment PSPP - a program for statistical analysis.
=for comment Copyright (C) 2019 Free Software Foundation, Inc.
=for comment
=for comment This program is free software: you can redistribute it and/or modify
=for comment it under the terms of the GNU General Public License as published by
=for comment the Free Software Foundation, either version 3 of the License, or
=for comment (at your option) any later version.
=for comment
=for comment This program is distributed in the hope that it will be useful,
=for comment but WITHOUT ANY WARRANTY; without even the implied warranty of
=for comment MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
=for comment GNU General Public License for more details.
=for comment
=for comment You should have received a copy of the GNU General Public License
=for comment along with this program. If not, see <http://www.gnu.org/licenses/>.
=head1 PSPP::Examples
This page shows some simple examples of using the PSPP module.
See L<PSPP> for details on each of the subroutines.
=head2 A Simple example
This example creates a system file called F<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();
=head2 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();
=head2 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");
=head2 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();
=head2 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();
=head2 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 C<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";
}
=cut
|
