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

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 final result array must contain [5, 20, 15].

score 4 · Accepted Answer · edited May 23 '17 at 10:24

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));

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
)

score 0 · Answer 2 · answered Aug 29 '21 at 17:43

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,
)

2 Answers2