PHP Functions Essential Reference

array_rand

mixed array_rand(array array, [int num_elements]) 

array	Array from which to pick random elements
num_elements	Number of elements to pick at random

Returns one or more keys at random from an array.

Returns:

Key or array of keys of random elements of an array; NULL on failure

Description:

This function selects num_elements elements at random from the array given by array and returns their keys as elements in a new array. If num_elements is 1 or omitted, a single key is returned. Otherwise, an indexed array is returned; the selected keys are the element values in the returned array.

Since array_rand() internally uses the rand() function, you should use srand() before calling array_rand() to ensure the greatest possible randomness. ...