1,
2,
3,

##</code><code>##

1,10,20,30,40,
1,15,25,35,45,
2,3,5,6,7,8,
3,100,200,300,400
2,10,4,-8,16,32
3,300,400,500,600

##</code><code>##

#!/usr/bin/perl

use strict;
use warnings;

use feature 'say';

use Text::CSV;
use List::Util qw 'sum';

my @IDs;
my $IDfile = 'ids.csv';
my $Intfile = 'interactions.csv';

my $csv = Text::CSV->new() or die "Can't use CSV: " . Text::CSV->error_diag();

# Open file containing IDs
# our example has id's in the first column

my $fh;
open( $fh, '<', $IDfile ) or die "Can't open $IDfile: $!";

# build an array of IDs for processing;

while ( my $row = $csv->getline( $fh ) ){

  push @IDs, $row->[0];

}

# close csv
$csv->eof or $csv->error_diag();
close $fh;

# parse interactions

open ( $fh, '<', $Intfile ) or die "Can't open $Intfile: $!";

my $data = $csv->getline_all($fh);

$csv->eof or $csv->error_diag();
close $fh;

# for each ID in our array

foreach my $ID ( @IDs ){

  my @total;

  # loop through interactions data

  foreach my $row ( @$data ){

    # if the fist column is equal to the value of $ID
    if ( $row->[0] == $ID ){

      # add the value of the fourth column to the array
      push @total, $row->[3];
    }
  }

  # display totals
  say "Total for ID $ID: " . sum( @total ) if ( @total );
}

##</code><code>##

Total for ID 1: 65
Total for ID 2: -2
Total for ID 3: 800