php - Sum time if date already exists or has a duplicate -

i have array

$date = array{"2013-09-17 00:21:00",               "2013-09-23 00:12:00",               "2013-09-23 00:41:00",               "2013-09-20 00:13:00",               "2013-09-19 00:34:00",               "2013-09-17 00:38:00"} 

i'm trying sum time inside array have same date.

this expected output:

 $date = array{"2013-09-17 00:59:00",                "2013-09-23 00:53:00",                 "2013-09-20 00:13:00",                "2013-09-19 00:34:00"} 

now have tried far

foreach($date $key => $value)         {             $lf_date[] = date("y-m-d",strtotime($value));             $lf_time[] = date("h:i:s",strtotime($value));              if(isset($lf_date[$key]))             {                  $output[] += $lf_time[$key];              }             else             {                  $output[] = $lf_time[$key];              }          } 

this gives me 0 output t_t.. tried searching on google , says have use isset , array_key_exists can't work. :(. me.

use:

<?php $date = array("2013-09-17 00:21:00",               "2013-09-23 00:12:00",               "2013-09-23 00:41:00",               "2013-09-20 00:13:00",               "2013-09-19 00:34:00",               "2013-09-17 00:38:00");  $array = array();              foreach($date $key => $value) {     $lf_date = date("y-m-d",strtotime($value));     $lf_time = date("h:i:s",strtotime($value));      $midnight = strtotime("0:00");      if(!isset($array[$lf_date]))             $array[$lf_date] = 0;//check array index exists      $array[$lf_date] += strtotime($lf_time) - $midnight; }  foreach($array $key => $value) {     $midnight = strtotime("0:00");     $array[$key] = $key." ".date("g:i:s", $midnight + $value); }  $result = array_values($array);  print_r($result);  ?> 

output:

array (     [0] => 2013-09-17 0:59:00     [1] => 2013-09-23 0:53:00     [2] => 2013-09-20 0:13:00     [3] => 2013-09-19 0:34:00 )