The challenge is only to iterate all the 2-member subsets of the set on a per line basis. For example:
use Data::Dumper;
my %pairs = ();
while (<>) {
    chomp;
    my @found = split;
    for my $k1 ( @found );
        for my $k2 ( @found ) {
            if ( $k2 gt $k1 ) { # ensuring each pair is counted once o
+nly for the line
                $pairs{ $k1 }{ $k2 }++;
            }
        }
    }
} 
print Dumper \%pairs;

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(updated thanks to syntax catch by Wind)

One world, one people

In reply to Re: counting pairwise incidences by anonymized user 468275
in thread counting pairwise incidences by reubs85

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