php: sort and count instances of words in a given string

Use a combination of str_word_count() and array_count_values():

$str="happy beautiful happy lines pear gin happy lines rock happy lines pear ";
$words = array_count_values(str_word_count($str, 1));
print_r($words);

gives

Array
(
    [happy] => 4
    [beautiful] => 1
    [lines] => 3
    [pear] => 2
    [gin] => 1
    [rock] => 1
)

The 1 in str_word_count() makes the function return an array of all the found words.

To sort the entries, use arsort() (it preserves keys):

arsort($words);
print_r($words);

Array
(
    [happy] => 4
    [lines] => 3
    [pear] => 2
    [rock] => 1
    [gin] => 1
    [beautiful] => 1
)