investigate Data::Frame subset P2R conversion bug

[zmughal]

Creating a Data::Frame and sending it to R gives completely wrong values. This is probably something in the PDL API.

[zmughal]

This is probably because the PDL data needs to be a copy (using ->copy or ->sever). A work around was needed for

my $s = sequence(4, 10);
my $p = Data::Frame->new( columns => [
                 a => $s->slice('(0)')->copy,  # using copy because there is a bug in the PDL
                 b => $s->slice('(1)')->copy,  # conversion in Statistics::NiceR
                 c => $s->slice('(2)')->copy,
                 d => $s->slice('(3)')->copy,
] );
use DDP; p Statistics::NiceR->new->as_matrix( $p );