Count multi array rates - php

Question

Im having troubles counting this.
I want to count all rates than belongs to id_image.
Maybe like key = id_image and value = tot count, id tried with array_count_values, but i cant use it normally when its multi :-S
Array
(
[0] => Array
(
[id_image] => 12
[rate] => 4
)
[1] => Array
(
[id_image] => 13
[rate] => 4
)
[2] => Array
(
[id_image] => 14
[rate] => 3
)
[3] => Array
(
[id_image] => 13
[rate] => 4
)
[4] => Array
(
[id_image] => 12
[rate] => 5
)
[5] => Array
(
[id_image] => 12
[rate] => 4
)
)

Answer 1

// test array
$arr = array(
0 => array(
'id_image' => 1,
'rate' => 3
),
1 => array(
'id_image' => 2,
'rate' => 8
),
2 => array(
'id_image' => 3,
'rate' => 4
),
3 => array(
'id_image' => 1,
'rate' => 2
),
4 => array(
'id_image' => 3,
'rate' => 2
)
);
// put the length in a var so we don't keep calling count();
$length = count($arr);
// the new array that'll hold the sum of the rates
$totals = array();
// iterate through the test array
for ($i = 0; $i < $length; ++$i) {
// check if $totals already contains data for the specified id_image
if (isset($totals[$arr[$i]['id_image']])) {
// if so, add data
$totals[$arr[$i]['id_image']] += $arr[$i]['rate'];
} else {
// if not so, set data
$totals[$arr[$i]['id_image']] = $arr[$i]['rate'];
}
}
var_dump($totals);
Example