SLOYD / Alt-Data-Frame-ButMore-0.0042_01 / lib / Data / Frame / Role / Rlike.pm 

            

              
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package Data::Frame::Role::Rlike;
use Data::Frame::Role;
use List::AllUtils;
method head($n=6) {
        my ($start, $stop);
        if( $n < 0 ) {
                $start = 0;
                $stop = $self->number_of_rows + $n - 1;
        } else {
                $start = 0;
                $stop  = $n - 1;
        }
        # clip to [ 0, number_of_rows-1 ]
        $start = List::AllUtils::max( 0, $start );
        $stop  = List::AllUtils::min( $self->number_of_rows-1, $stop );
        return $self->select_rows( $start..$stop );
}
method tail($n=6) {
        my ($start, $stop);
        if( $n < 0 ) {
                $start = -$n;
                $stop = $self->number_of_rows - 1;
        } else {
                $start = $self->number_of_rows - $n;
                $stop = $self->number_of_rows - 1;
        }
        # clip to [ 0, number_of_rows-1 ]
        $start = List::AllUtils::max( 0, $start );
        $stop  = List::AllUtils::min( $self->number_of_rows-1, $stop );
        return $self->select_rows( $start..$stop );
}
sub subset($&) {
        my ($df, $cb) = @_;
        my $ch = $df->_column_helper;
        local *_ = \$ch;
        my $where = $cb->($df);
        $df->select_rows( $where->which );
}
1;
__END__
=pod
=encoding UTF-8
=head1 NAME
Data::Frame::Role::Rlike
=head1 VERSION
version 0.0042_01
=head1 SYNOPSIS
Data::Frame::Role::Rlike - role to provide R-like methods for Data::Frame
=head1 METHODS
=head2 head
    head( Int $n )
If $n ≥ 0, returns a new C<Data::Frame> with the first $n rows of the
C<Data::Frame>.
If $n < 0, returns a new C<Data::Frame> with all but the last -$n rows of the
C<Data::Frame>.
See also: R's L<head|https://stat.ethz.ch/R-manual/R-devel/library/utils/html/head.html> function.
=head2 tail
    tail( Int $n )
If $n ≥ 0, returns a new C<Data::Frame> with the last $n rows of the
C<Data::Frame>.
If $n < 0, returns a new C<Data::Frame> with all but the first -$n rows of the
C<Data::Frame>.
See also: R's L<tail|https://stat.ethz.ch/R-manual/R-devel/library/utils/html/head.html> function.
=head2 subset
    subset( CodeRef $select )
C<subset> is a helper method used to take the result of a the C<$select>
coderef and use the return value as an argument to
L<C<select_rows>/Data::Frame#select_rows>>.
The argument C<$select> is a CodeRef that is passed the Data::Frame
    $select->( $df ); # $df->subset( $select );
and returns a PDL. Within the scope of the C<$select> CodeRef, C<$_> is set to
a C<Data::Frame::Column::Helper> for the Data::Frame C<$df>.
    use Data::Frame::Rlike;
    use PDL;
    my $N  = 5;
    my $df = dataframe( x => sequence($N), y => 3 * sequence($N) );
    say $df->subset( sub {
                           ( $_->('x') > 1 )
                         & ( $_->('y') < 10 ) });
    # ---------
    #     x  y
    # ---------
    #  2  2  6
    #  3  3  9
    # ---------
See also: R's L<subset|https://stat.ethz.ch/R-manual/R-devel/library/base/html/subset.html> function
=head1 AUTHORS
=over 4
=item *
Zakariyya Mughal <zmughal@cpan.org>
=item *
Stephan Loyd <sloyd@cpan.org>
=back
=head1 COPYRIGHT AND LICENSE
This software is copyright (c) 2014, 2019 by Zakariyya Mughal, Stephan Loyd.
This is free software; you can redistribute it and/or modify it under
the same terms as the Perl 5 programming language system itself.
=cut