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### Re: Set intersection problem

by tybalt89 (Monsignor)
 on May 23, 2023 at 15:00 UTC Need Help??

in reply to Set intersection problem

I'm not sure I understand your problem, but my guess goes something like this:

```#!/usr/bin/perl

use strict; # https://perlmonks.org/?node_id=11152381
use warnings;

my %sets = ( A => [1,2,3], B => [3, 4], C => [1, 3, 4] );
use Data::Dump 'dd'; dd 'original sets', \%sets;

my %intersection;
for my \$setname ( keys %sets )
{
\$intersection{\$_}{\$setname}++ for @{ \$sets{\$setname} };
}
use Data::Dump 'dd'; dd 'intersection', \%intersection;

print "items in more than one set:\n";
for my \$setname ( sort keys %intersection )
{
if( 1 < keys %{ \$intersection{\$setname} } )
{
my \$where = join ' and ', map "'\$_'",
sort keys %{ \$intersection{\$setname} };
print "    '\$setname' is in \$where\n";
}
}

Outputs (complete with intermediate calculations):

```(
"original sets",
{ A => [1, 2, 3], B => [3, 4], C => [1, 3, 4] },
)
(
"intersection",
{
1 => { A => 1, C => 1 },
2 => { A => 1 },
3 => { A => 1, B => 1, C => 1 },
4 => { B => 1, C => 1 },
},
)
items in more than one set:
'1' is in 'A' and 'C'
'3' is in 'A' and 'B' and 'C'
'4' is in 'B' and 'C'

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