Flatten a multidimensional PDO array into an indexed array when fetching a single column

flattenPDOArray.php

/**
 * Flatten array of PDO results into a single dimension.
 * Note: This is only useful for a PDO query returning a single column (you probably don't want to do this otherwise).
 *
 * @param array $arrayToFlatten
 * @return array
 */
public function flattenArray($arrayToFlatten, $key)
{
    // Set up array.
    $newArray = [];

    foreach ($arrayToFlatten as $index => $value) {
        $newArray[$index] = $value[$key];
    }

    return $newArray;
}