array_chunk() splits the array
into several arrays with
size values in them. You may also have an array with
less values at the end. You get the arrays as members of a
multidimensional array indexed with numbers starting from
zero.
By setting the optional
preserve_keys parameter to
TRUE, you can force PHP to preserve the original
keys from the input array. If you specify FALSE new number indices will be used
in each resulting array with indices starting from zero. The
default is FALSE.