Looking through the available functions in the API, I cannot find one that will start an array from empty again.
If I remember correctly:
$myarray = array();
You just set your variable to a new blank array.
$array = array();
In most cases, just assign a new array:
$ar = array();
If you really want to modify the array in-place, use array_splice:
array_splice($ar, 0, count($ar));
$myarray=array(); // Reset $myarray to an empty array.
Also, don't use unset( $array ); The execution time is way longer than = array();
Nowadays (actually, since 2012) we can use:
$array = [];
More elegant and consistent with other languages.