Get all corresponding keys for repeated elements

I have a file which consists of 开发者_JS百科following:

A  1
A  2
B  3
B  4
B  5
B  6
C  7
A  8  

I want to get all unique keys in first column, but get all corresponding values for that unique key, i.e I need to get:

A 1,2,8
B 3,4,5,6
C 7

What would be the best way to do this?

(I've heard that Perl has good support to solve this, but I'm new to Perl.)

try this:

open my $fh, '<', "data_filename";
my %map;

while(my $line = <$fh>) {
  my ($key, $val) = split(/\s+/, $line);
  push @{$map{$key}}, $val;
}

You probably want a hash, where each value in the hash is an array reference.

my %values;
while (<>) {
    my ($left, $right) = split(/ /,$_,2);
    my $array = $values{$left};
    if (!$array) {
        $array = [];
        $values{$left} = $array;
    }
    push(@{$array},$right);
}

You can verify that this has produced the correct data structure with Data::Dumper:

use Data::Dumper;
print Dumper(\%values);

This is just another possible solution for the sake of completeness. In this case, the hash stores a the key and a string containing your values.

use warnings;
use strict;

my %hash = ();
open (FILE, "input.txt") or die "";
while(FILE>){
chomp;
(my $key, my $value) = split;
    $value = ",".$value if exists $hash{$key};
    $hash{$key}.= $value;
}

foreach my $key (sort keys %hash){
    print "$key $hash{$key}\n";
}

As always, there's more than one way to do it.