wp_list_pluck.function.php

<?php
/**
 * Pluck a certain field out of each object in a list.
 *
 * This has the same functionality and prototype of
 * array_column() (PHP 5.5) but also supports objects.
 *
 * @param array      $list      List of objects or arrays
 * @param int|string $field     Field from the object to place instead of the entire object
 * @param int|string $index_key Optional. Field from the object to use as keys for the new array.
 *                              Default null.
 * @return array Array of found values. If `$index_key` is set, an array of found values with keys
 *               corresponding to `$index_key`. If `$index_key` is null, array keys from the original
 *               `$list` will be preserved in the results.
 */
function wp_list_pluck( $oldlist, $field, $index_key = null ) {
	$newlist = array();

	if ( ! $index_key ) {
		/*
		 * This is simple. Could at some point wrap array_column()
		 * if we knew we had an array of arrays.
		 */
		foreach ( $oldlist as $key => $value ) {
			if ( is_object( $value ) ) {
				$newlist[ $key ] = $value->$field;
			} else {
				$newlist[ $key ] = $value[ $field ];
			}
		}

		return $newlist;
	}

	/*
	 * When index_key is not set for a particular item, push the value
	 * to the end of the stack. This is how array_column() behaves.
	 */
	foreach ( $oldlist as $value ) {
		if ( is_object( $value ) ) {
			if ( isset( $value->$index_key ) ) {
				$newlist[ $value->$index_key ] = $value->$field;
			} else {
				$newlist[] = $value->$field;
			}
		} else {
			if ( isset( $value[ $index_key ] ) ) {
				$newlist[ $value[ $index_key ] ] = $value[ $field ];
			} else {
				$newlist[] = $value[ $field ];
			}
		}
	}

	return $newlist;
}