Get max value from each column of a 2-dimensional array - php

Question

I have an array within an array, for example:
[
[0, 20, 5],
[5, 0, 15],
[5, 10, 0]
]
I need to get the max number in each column.
The max of [0 , 5 , 5] is 5, so that goes into the result array.
The max of [20, 0, 10] is 20, so that goes into the result array.
The max of [5, 15, 0] is 15, so that goes into the result array.
The final result array must contain [5, 20, 15].

Answer 1

First, the array has to be transposed (flip the rows and columns):
function array_transpose($arr) {
$map_args = array_merge(array(NULL), $arr);
return call_user_func_array('array_map', $map_args);
}
(taken from Is there better way to transpose a PHP 2D array? - read that question for an explanation of how it works)
Then, you can map the max function on the new array:
$maxes = array_map('max', array_transpose($arr));
Example: http://codepad.org/3gPExrhO
Output [I think this is what you meant instead of (5, 15, 20) because you said index 1 should be max of (20, 0, 10)]:
Array
(
[0] => 5
[1] => 20
[2] => 15
)

Answer 2

Without the splat operator, array_map() with max() will return the max value for each row. ([20, 15, 10])
With the splat operator to transpose the data structure, the max value for each column is returned.
Code: (Demo)
$array = [
[0, 20, 5],
[5, 0, 15],
[5, 10, 0]
];
var_export(
array_map('max', ...$array)
);
Output:
array (
0 => 5,
1 => 20,
2 => 15,
)