Find for each sub array in multidimensional array, if element on fixed position is highest value for this sub array

Hello all.

For each sub array in $arr_rgb (Fig.01) I have to find: If element with $key number 1 is the highest number in this sub array, then return the $key number of the sub array (Fig.03 and Fig.04. So far, I can find highest number for each sub array – fig.02

In the attached image the “trouble” I have is explained.

And the code that I use so far:

<?php
$hex_splited = [
        ['00','00','00'], 
        ['10', '11', '10'], 
        ['F0', '1A', 'C3'],
        ['0F', 'FE', 'F4'],
       ];

$arr_rgb = [];
$count2 = count($hex_splited);

for ($i=0; $i < $count2; $i++) { 
    
    $inn_count = count($hex_splited[$i]);
    
    for ($j=0; $j < $inn_count; $j++) { 
            
        $val = hexdec($hex_splited[$i][$j]);
        $arr_rgb[$i][$j] = $val;

        foreach ($arr_rgb as $key => $value) {
            $resultMax[$key] = max($value);
        }
    }
}

echo "<pre>";
var_dump($resultMax);
echo "</pre>";

    echo "<table border='1'>";
for ($m=0; $m < $count2; $m++) {
    echo "<tr>";
    for ($k=0; $k < $inn_count; $k++) { 
        echo "<td>";
        echo $arr_rgb[$m][$k];
        echo "</td>";
    }
    echo "</tr>";
}
echo "</table>";

Answer

Determining the maximum using max only properly works for integers, so I would use array_map with hexdec to achieve that.

Then all it needs is a comparison of the value at position 1 with that maximum, and if they are the same, then the index gets added to the result array:

$result = [];
foreach($hex_splited as $key => $value) {
  if(hexdec($value[1]) == max(array_map('hexdec', $value))) {
    $result[] = $key;
  }
}
var_dump($result);

This gets you 0, 1, 3 as result. (As IMHO it should be, according to your stated requirements – the value 00 at position 1 in the first sub-array is also the maximum of all values in that sub-array. If you need to exclude 0 values, then you’ll have to modify accordingly.)

EDIT:

if all elements are equal, then return nothing

Okay, that can also be implemented quite easily – we use array_count_values, and if the count of that is only 1, then that means all the elements had the exact same value.

So then it becomes

foreach($hex_splited as $key => $value) {
  if(count(array_count_values($value)) != 1 &&
      hexdec($value[1]) == max(array_map('hexdec', $value))) {
    $result[] = $key;
  }
}

With that, you get [1, 3] as $result here.