use Modern::Perl;
use Data::Dump qw(dump);

my %result;
for (<DATA>) {
	my ($key,$num) = split /,/;
	$result{$key} += $num;
}

say dump \%result;

__DATA__
2010-02-12_aaa,902
2010-02-12_bbb,374
2010-02-12_ccc,158
2010-02-13_aaa,745
2010-02-13_bbb,1140
2010-02-13_ddd,852
2010-02-14_bbb,754
2010-02-14_aaa,169
2010-02-14_ccc,1721

{
  "2010-02-12_aaa" => 902,
  "2010-02-12_bbb" => 374,
  "2010-02-12_ccc" => 158,
  "2010-02-13_aaa" => 745,
  "2010-02-13_bbb" => 1140,
  "2010-02-13_ddd" => 852,
  "2010-02-14_aaa" => 169,
  "2010-02-14_bbb" => 754,
  "2010-02-14_ccc" => 1721,
}