php - Get index for multi-dimensional array -

i need index of multidimensional , output variable. know simple struggling it.

for example given following:

[1]=>   array(11) {     ["field_label"]=>     string(24) "what first name?"     ["field_name"]=>     string(6) "f_name"     ["identifier"]=>     bool(true)     ["options"]=>     bool(false)     ["form_name"]=>     string(12) "demographics"   }   [2]=>   array(11) {     ["field_label"]=>     string(23) "what last name?"     ["field_name"]=>     string(6) "l_name"     ["identifier"]=>     bool(true)     ["options"]=>     bool(false)     ["form_name"]=>     string(12) "demographics"   } [3]=>   array(11) {     ["field_label"]=>     string(32) "researcher took measurements"     ["field_name"]=>     string(17) "weight_researcher"     ["identifier"]=>     bool(false)     ["options"]=>     bool(false)     ["form_name"]=>     string(6) "weight"   } 

i want find index first element has form_name of "weight" (#3)

just use foreach , if inside it:

foreach($array $key => $value) {                //  ^ here resides key of parent array     if($value['form_name'] == 'weight') { // if form name weight         echo $key; // echo key         break; // stop on first occurence     } }