Introduction to PHP.

Arrays.

Arrays in PHP are unlike those of any other common programming language

Best described as a melding of the arrays of C/Java with the hashes of Perl

The ultimate in flexible built-in data structures!!

Like a Perl hash, arrays in PHP have two parts: a key and a value

If the keys are positive integers and in ascending order,

the array has similar logical structure to an array in another language

If the keys are keys are strings and the order is determined by a hashing function

the array has similar logical structure to a Perl hash array

PHP arrays can have some elements with integer keys and some with string keys

Array Creation

Assigning a value to an array that does not yet exist, creates the array

$list[0] =17;

$list[2]="This is a nice day";
$list[]=33;  #this element key will be 3

Using the array construct

$list2 = array(12, 34, 45, 56); 
	/* traditional array with 4 elements
	   with the keys 0, 1, 2, 3 */

$list3 = array( 1 => 12, 3 => 34, 4 => 45, 7 => 56);
	/* an array with four elements
	   with the keys 1, 3, 4, 7 */

$list4 = array();  # an empty array

$list5 = array("Tom" => 13, "Dick" => 18, "Jerry" => 24);
	/* an array with three elements
	   with the keys "Tom", "Dick", "Jerry" */

$list6 = array( "make" => "volvo", "model" => "245",
		"year" => 1974, 3 => "Sold" );
	/* PHP arrays can be mixtures of
	   tarditional arrays and hashes */

Accessing Array Elements

Array elements are accessed by subscripting

$val = $list3[3];  # $val has a value of 34

$val = $list5['Tom']; # $val is 13

$val = $list6[3]; # $val is "Sold"

The list construct works just like in Perl

The array_keys function takes an array and returns the array keys

$keys6 = array_keys($list6);
	/* $keys6 holds the keys of $list6 */
$valu6 = array_values($list6);  
	/* $valu6 holds the values of $list6 */

Dealing with Arrays

Sequential Access to Array Elements

Sorting Arrays
- sort
  
  Sorts the values of the array replacing the keys
  
  The string values migrate to the beginning of the array in alpha order
  
  The numeric values follow in ascending order
  
  The new keys are sequential: 0, 1, ...
- sort with SORT_NUMERIC
  
  The numeric values are sorted in ascending order
  
  The string values migrate to the beginning of the array unsorted
- asort
  
  Sorts hashes, values are sorted
  
  Keeps key => value association
- rsort
  
  Reverse order sort
- arsort
  
  Reverse order asort

<!DOCTYPE HTML PUBLIC "-//W3C//DTD XHTML 1.0 strict//EN"
"http://www.w3.org/TR/xhtml1/dtd/xhtml1-strict.dtd">

                                                    
<!--	sorting.php
	An example to illustrate sorting functions
	-->

<html>
<head>
<title>
Sorting Functions
</title>
</head>

<body>
<?php
$original = array("Fred"=> 31, "Al" => 27, "Gandalf" => "wizzard",
		"Betty" => 42, "Frodo" => "hobbit" );
?>
<h4>Original Array</h4>
<?php
foreach ($original as $key => $value )
	print("[$key] => $value <br />");

$new = $original;
sort($new);
?>

<h4>Array Sorted by <tt>sort</tt></h4>
<?php
foreach ($new as $key => $value )
	print("[$key] => $value <br />");

$new = $original;
sort($new,  SORT_NUMERIC);
?>

<h4>Array Sorted by <tt>sort,  SORT_NUMERIC</tt></h4>
<?php
foreach ($new as $key => $value )
	print("[$key] => $value <br />");

$new = $original;
rsort($new);
?>

<h4>Array Sorted by <tt>rsort</tt></h4>
<?php
foreach ($new as $key => $value )
	print("[$key] => $value <br />");

$new = $original;
asort($new);
?>

<h4>Array Sorted by <tt>asort</tt></h4>
<?php
foreach ($new as $key => $value )
	print("[$key] => $value <br />");

$new = $original;
arsort($new);
?>

<h4>Array Sorted by <tt>arsort</tt></h4>
<?php
foreach ($new as $key => $value )
	print("[$key] => $value <br />");
?>
</body>
</html>

An example to illustrate sorting fucntions