The following should be self-explanatory. Ask if you have questions.

use strict;
use warnings;

my @data;

<DATA>; # Skip header.

while (<DATA>) {
   chomp;
   push(@data, [ map { 0+$_ } split(/\t/, $_) ]);
}

# Sort by "In".
my @in_sorted = sort { $a->[1] <=> $b->[1] } @data;

# Sort by "Out".
my @out_sorted = sort { $a->[2] <=> $b->[2] } @data;

# Sum "In" and "Out" by "Day".
my %in_day;
my %out_day;
foreach (@data) {
   my $day = $_->[3];

   # Avoid warnings.
   $in_day{$day}  ||= 0;
   $out_day{$day} ||= 0;

   $in_day{$day}  += $_->[1];  # "In"
   $out_day{$day} += $_->[2];  # "Out"
}

__DATA__
ID    In    Out    Day
1    5    2    1
2    4    9    2
3    3    3    2
4    6    7    3
5    5    0    5
6    7    9    3
7    8    9    4
8    6    6    4

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In reply to Re: Tabular Data, Group By Functions by ikegami
in thread Tabular Data, Group By Functions by Anonymous Monk

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