PHP: Arrays

Derek Bridge

Department of Computer Science,
University College Cork

PHP: Arrays

Aims:

• to learn about indexed arrays in PHP
• to learn about associative arrays in PHP

Indexed arrays

• An indexed array (or just array) is a collection of values, indexed by position (starting from 0)
• To create an indexed array in PHP, e.g.:

  $extraToppings = array('mushrooms', 'anchovies', 'chocolate');

• Another way to create an indexed array, e.g.

  $extraToppings[0] = 'mushrooms';
$extraToppings[1] = 'anchovies';
$extraToppings[2] = 'chocolate';

Doing things to indexed arrays

• Inserting a value into the end of an existing array, e.g.:

  $extraToppings[] = 'baked beans';

• Modifying a value in an existing array, e.g.

  $extraToppings[1] = 'fried egg';

• Accessing a value in an array, e.g.

  $firstTopping = $extraToppings[0];
echo "My favourite topping is: {$extraToppings[2]}";


Doing things to each value in an indexed array

foreach ($a as $v)
{
  ...do something to $v...
}


This is a loop which visits each value in array $a in turn, referring to them as $v

You may have any number of statements within the braces

Doing things to each value in an indexed array

<?php
 echo "<ul>";
 foreach ($extraToppings as $topping) 
 {
   echo "<li>{$topping}</li>";
 }
 echo "</ul>"; 
?>

Associative arrays

• An associative array is a collection of keys and values, where each key is associated with one value (a map!)
• To create an associative array in PHP, e.g.:

  $prices = array('Apples' => 1.59, 'Pears' => 2.34,
   'Kumquats' => 4.05, 'Jujubes' => 2.34);

• Or

  $prices['Apples'] = 1.59;
$prices['Pears'] = 2.34;
$prices['Kumquats'] = 4.05;
$prices['Jujubes'] = 2.34;

Doing things to associative arrays

• Inserting a key and value an existing array, e.g.:

  $prices['Mangoes'] = 5.26;

• Modifying a value in an existing array, e.g.

  $prices['Kumquats'] = 3.93;

• Accessing a value in an array, e.g.

  $priceOfPears = $prices['Pears'];
echo "The price of mangoes is: {$prices['Mangoes']}";

Doing things to each value in an associative array

foreach ($a as $k => $v)
{
  ...do something to $k and/or $v...
}


This is a loop which visits each key and value in array $a in turn, referring to them as $k and $v

You may have any number of statements within the braces

Doing things to each value in an associative array

<table>
 <tr><th>Fruit</th><th>Price</th></tr>
<?php
  foreach ($prices as $fruit => $price) 
  {
    echo "<tr>
           <td>{$fruit}</td>
           <td>{$price}</td>
         </tr>";
  }
?>
</table>

PHP's 84+ built-in functions for arrays

• For indexed arrays,
  • sort($a) sorts array $a into ascending order (use rsort for descending order)
• For associative arrays,
  • ksort($a) sorts array $a into ascending order of its keys (or krsort for descending order)
  • asort($a) sorts array $a into asending order of its values (or arsort for descending order)
  • array_keys($a) returns an indexed array containing just the keys of $a
  • array_values($a) returns an indexed array containing just the values of $a

One of PHP's predefined associative arrays

• $_SERVER is a predefined associative array containing lots of info from the web server
• Keys may include:

  SERVER_SOFTWARE

  A string that identifies the server

  HTTP_USER_AGENT

  The string the browser used to identify itself

  REQUEST_METHOD

  The command (method) used by the client (e.g. GET)

  ...and lots more (although they may depend on your version of PHP)

One of PHP's predefined associative arrays

It's easy to output the contents of the $_SERVER array as a table, one row per key/value

<table>
<?php
  foreach ($_SERVER as $variable => $value) 
  {
    echo "<tr>
           <th>{$variable}:</th>
           <td>{$value}</td>
         </tr>";
  }
?>
</table>

Class exercise

Write a PHP script that outputs the contents of the $_SERVER array as a table, but this time let's have one column per key/value