use strict;
use warnings;

my @events_aray = (1, 3, 3, 4, 5, 5);
my %days;

++$days{$_} for @events_aray;

print "date $_ appeared $days{$_} times\n"
    for sort {$a <=> $b} keys %days;

##</code><code>##

date 1 appeared 1 times
date 3 appeared 2 times
date 4 appeared 1 times
date 5 appeared 2 times