php index of item

Try the array_search function.

From the first example in the manual:

<?php
$array = array(0 => 'blue', 1 => 'red', 2 => 'green', 3 => 'red');

$key = array_search('green', $array); // $key = 2;
$key = array_search('red', $array);   // $key = 1;
?>

A word of caution

When comparing the result, make sure to test explicitly for the value false using the === operator.

Because arrays in PHP are 0-based, if the element you’re searching for is the first element in the array, a value of 0 will be returned.

While 0 is a valid result, it’s also a falsy value, meaning the following will fail:

<?php
    $array = array(0 => 'blue', 1 => 'red', 2 => 'green', 3 => 'red');   

    $key = array_search('blue',$array);

    if($key == false) {
        throw new Exception('Element not found');
    }
?>

This is because the == operator checks for equality (by type-juggling), while the === operator checks for identity.