Page 195 - Beginning PHP 5.3

Chapter 7: Functions
How It Works
After displaying an XHTML page header, the script sets up a $myText variable that holds the text
whose words are to be sorted. (Feel free to replace the example text with your own.) It then displays
the text within a fixed-width HTML div element.

Next, the script gets to work on processing the text. First it uses PHP’s preg_replace() function to
strip out all commas and periods from the text:

$myText = preg_replace( “/[\,\.]/”, “”, $myText );
(This line of code uses a simple regular expression to do its job; you learn more about preg_
replace() and regular expressions in Chapter 18.)
The next line of code calls the PHP function preg_split() to split the string into an array of words,
using any of the whitespace characters \n, \r, \t and space to determine the word boundaries. It then
processes the array through PHP’s handy array_unique() function, which removes any duplicate
words from the array:
$words = array_unique( preg_split( “/[ \n\r\t]+/”, $myText ) );

preg_split() splits a string by using a regular expression to locate the points at which to split. Find
out more about preg_split() in Chapter 18 .

Next comes the sorting logic, and this is where anonymous functions come into play. The script uses
PHP ’ s usort() function to sort the array of words. usort() expects an array to sort, followed by a
callback comparison function. All comparison functions need to accept two values — $a and $b — and

return one of three values:
❑ A negative number if $a is considered to be “ less than ” $b
❑ Zero if $a is considered to be “ equal to ” $b
❑ A positive number if $a is considered to be “ greater than ” $b

In this case, the comparison function needs to determine if the length of the string $a is less than, equal
to, or greater than the length of the string $b . It can do this simply by subtracting the length of $a from
the length of $b and returning the result. (Remember from Chapter 5 that PHP ’ s strlen() function
returns the length of a string.)

Here, then, is the complete line of code to sort the array:
usort( $words, create_function( ‘$a, $b’, ‘return strlen($a) - strlen($b);’ ) );

Notice that this line of code uses the create_function() function to create an anonymous comparison
function, which is in turn used by usort() to sort the array.

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