determine average value from an array column - php

Question

consider below array:-
Array
(
[0] => Array
(
[0] => 99895
[1] => 35378
[2] => 0.01
)
[1] => Array
(
[0] => 99895
[1] => 813
[2] => -0.97
)
[2] => Array
(
[0] => 99895
[1] => 771
[2] => 0.29
)
[3] => Array
(
[0] => 442
[1] => 833
[2] => -1.06
)
[4] => Array
(
[0] => 442
[1] => 485
[2] => -0.61
)
[5] => Array
(
[0] => 442
[1] => 367
[2] => -0.14
)
[6] => Array
(
[0] => 442
[1] => 478
[2] => 0.77
)
[7] => Array
(
[0] => 442
[1] => 947
[2] => -0.07
)
[8] => Array
(
[0] => 7977
[1] => 987
[2] => 0.76
)
[9] => Array
(
[0] => 7977
[1] => 819
[2] => 0.37
)
[10] => Array
(
[0] => 7977
[1] => 819
[2] => 0.36
)
[11] => Array
(
[0] => 7977
[1] => 653
[2] => 1.16
)
[12] => Array
(
[0] => 7977
[1] => 1653
[2] => 1.15
)
)
from the above array how will I determine the below array?
array
(
99895 => -0.223
442 => -0.22
7977 => 0.76
)
Actually I need the average value of column 3 in respect of column 1.

Answer 1

First collect all the column 3 elements into an array keyed off column 1:
$arrays = array();
foreach ($input as $vals) {
$key = $vals[0];
$val = $vals[2];
if (isset($arrays[$key])) {
$arrays[$key][] = $val;
} else {
$arrays[$key] = array($val);
}
}
Now go through all of them, calculating the averages:
foreach ($arrays as &$array) {
$array = array_sum($array)/count($array);
}