RE: http://stackoverflow.com/questions/12142144/php-arrays-summing-values-with-matching-dates

php array

$out = array();
$myArray=array(
      array(
            'date' => '2011-05-13',
            'value' => 2
        ),
    array(
            'date' => '2011-05-14',
            'value' => 5
        ),
        array(
            'date' => '2011-05-13',
            'value' => 7
        ),
    array(
            'date' => '2011-05-14',
            'value' => 3
        ),

);
// Looping over each input array item
foreach ($myArray as $elem) {
      $out[] = $elem['date'];
     $out[$elem['date']]['value'] += $elem['value'];

}

print_r($out);
//Array ( [0] => 2011-05-13 [1] => Array ( [value] => 9 ) [2] => 2011-05-14 [3] => Array ( [value] => 8 ) [4] => 2011-05-13 [5] => 2011-05-14 )