Please see Writeup Formatting Tips for info on how to properly format posts here. In this case, wrap code in <code> tags and paragraphs in <p> tags.

Use a hash, or more specifically a hash of arrays:

#! perl
use strict;
use warnings;
use Data::Dumper;

my @transactions = (
    'yadda 01 abc',
    'yadda 03 sss',
    'yadda 02 asdsdbc',
    'yadda 02 adfgbc',
    'yadda 01 abgxvc',
    'yadda 02 azdfbc',
    'yadda 04 azdfbc',
    'yadda 04 abdc',
);

my %results;
foreach (@transactions) {
    my ($number) = /\s(\d+)\s/;
    push @{$results{$number}}, $_;
}

print Dumper \%results;
[download]

which outputs:

$VAR1 = {
          '01' => [
                    'yadda 01 abc',
                    'yadda 01 abgxvc'
                  ],
          '03' => [
                    'yadda 03 sss'
                  ],
          '04' => [
                    'yadda 04 azdfbc',
                    'yadda 04 abdc'
                  ],
          '02' => [
                    'yadda 02 asdsdbc',
                    'yadda 02 adfgbc',
                    'yadda 02 azdfbc'
                  ]
        };
[download]

You could also accomplish the above using an array of arrays, relying on the employee number as your index. See perlretut and/or perllol. For a discussion of why to use this structure as opposed to a large number of differently named arrays, see Why it's stupid to use a variable as a variable name.