How to find the best matching key in a PHP array

Question

I have an associative array in php. the keys are integers. how do i find the nearest key to any integer input?

Answer 1

a simple, but brute force method:

$distance = 1000000;  // initialize distance as "far away"
foreach ($array as $idx => $value)
   if (abs ($idx - $target_index) < $distance)
   {
      $distance = abs ($idx - $target_index);
      $best_idx = $idx;
   }

Answer 2

If the array keys are in order, you can use a more efficient algorithm (which may or may not make an appreciable difference depending on what this is for and how big the arrays are):

$arr = [2 => 'a', 4 => 'b', 7 => 'c'];
$input = 5;

if (isset($arr[$input])) {
    return $input;
}

foreach ($arr as $key => $value) {
    if ($key > $input) {
        if (prev($arr) === FALSE) {
            // If the input is smaller than the first key
            return $key;
        }
        $prevKey = key($arr);

        if (abs($key - $input) < abs($prevKey - $input)) {
            return $key;
        } else {
            return $prevKey;
        }
    }