PHP array_flatten() function. Convert a multi-dimensional array into a single-dimensional array.

array_flatten.php

<?php 

/**
 * Convert a multi-dimensional array into a single-dimensional array.
 * @author Sean Cannon, LitmusBox.com | seanc@litmusbox.com
 * @param  array $array The multi-dimensional array.
 * @return array
 */
function array_flatten($array) { 
  if (!is_array($array)) { 
    return false; 
  } 
  $result = array(); 
  foreach ($array as $key => $value) { 
    if (is_array($value)) { 
      $result = array_merge($result, array_flatten($value)); 
    } else { 
      $result = array_merge($result, array($key => $value));
    } 
  } 
  return $result; 
}

For a simple 2D array:

$multiDimArray = [[1, 2], [3, 4], [5, 6]];
$flatArray = array_reduce($multiDimArray, 'array_merge', []);