PHP Programming/arrays

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Arrays

Arrays are sets of data which can be defined in a PHP Script. Arrays can contain other arrays inside of them without any restriction (hence building multidimensional arrays). Arrays can be referred to as tables or hashes.

Syntax

Arrays can be created in two ways. The first involves using the function array. The second involves using square brackets.

The array function method

In the array function method, you create an array in the scheme of:

$foo = bar()

For example, to set the array up to make the keys sequential numbers (Example: "0, 1, 2, 3"), you use:

 $foobar = array($foo, $bar);

This would produce the array like this:

 $foobar[0] = $foo
 $foobar[1] = $bar

It is also possible to define the key value:

 $foobar = array('foo' => $foo, 'bar' => $bar);

This would set the array like this:

 $foobar['foo'] = $foo
 $foobar['bar'] = $bar

The square brackets method

The square brackets method allows you to set up by directly setting the values. For example, to make $foobar[1] = $foo, all you need to do is:

 $foobar[1] = $foo;

The same applies for setting the key value:

 $foobar['foo'] = $foo;

Examples of Arrays

Example #1

This example sets and prints arrays.

PHP Code:

<?php
 $array = array("name"=>"Toyota","type"=>"Celica","colour"=>"black","manufactured"=>"1991");
 $array2 = array("Toyota","Celica","black","1991");
 $array3 = array("name"=>"Toyota","Celica","colour"=>"black","1991");
 print_r($array);
 print_r($array2);
 print_r($array3);
?>

PHP Output:

  Array
  (
      [name] => Toyota
      [type] => Celica
      [colour] => black
      [manufactured] => 1991
  )
  Array
  (
      [0] => Toyota
      [1] => Celica
      [2] => black
      [3] => 1991
  )
  Array
  (
      [name] => Toyota
      [0] => Celica
      [colour] => black
      [1] => 1991
  )

HTML Render:

Array ( [name] => Toyota [type] => Celica [colour] => black [manufactured] => 1991 ) Array ( [0] => Toyota [1] => Celica [2] => black [3] => 1991 ) Array ( [name] => Toyota [0] => Celica [colour] => black [1] => 1991 )

Example #2

The following example will output the identical text as Example #1:

<?php
  $array['name']="Toyota";
  $array['type']="Celica";
  $array['colour']="black";
  $array['manufactured']="1991";
 
  $array2[]="Toyota";
  $array2[]="Celica";
  $array2[]="black";
  $array2[]="1991";
 
  $array3['name']="Toyota";
  $array3[]="Celica";
  $array3['colour']="black";
  $array3[]="1991";
 
  print_r($array);
  print_r($array2);
  print_r($array3);
?>

Example #3

Using the Example #1 and Example #2 above, now you can try and use arrays the same way as normal variables:

PHP Code:

<?php
 echo "Manufacturer: &lt;b&gt;{$array['name']}&lt;/b&gt;&lt;br /&gt;\n";
 echo "Brand: &lt;b&gt;{$array2['1']}&lt;/b&gt;&lt;br /&gt;\n";
 echo "Colour: &lt;b&gt;".$array3['colour']."&lt;/b&gt;&lt;br /&gt;\n";
 echo "Year Manufactured: &lt;b&gt;".$array3[1]."&lt;/b&gt;&lt;br /&gt;\n"
?>

PHP Output:

 Manufacturer: <b>Toyota</b><br />
 Brand: <b>Celica</b><br />
 Colour: <b>black</b><br />
 Year Manufactured: <b>1991</b><br />

HTML Render:

Manufacturer: Toyota
Brand: Celica
Colour: black
Year Manufactured: 1991

Multidimensional Arrays

Elements in an array can also be an array, allowing for multidimensional arrays. An example, in accordance with the motoring examples above, is:

<?php
$cars = array(
   "car1" => array("make" => "Toyota","colour" => "Green","year" => 1999,"engine_cc" => 1998),
   "car2" => array("make" => "BMW","colour" => "RED","year" => 2005,"engine_cc" => 2400),
   "car3" => array("make" => "Renault","colour" => "White","year" => 1993,"engine_cc" => 1395),
);
?>

In this example, if you were to use:

<?php
echo "$cars['car1']['make']<br>";
echo "$cars['car3']['engine_cc']";
?>

The output would be:

Toyota
1395

Array Functions

There are dozens of array manipulation functions. Before implementing your own, make sure it doesn't already exist as a PHP function in Array functions (PHP manual entry).

Array traversal

In various circumstances, you will need to visit every array element and perform a task upon it.

The simplest and the most widely used method for this is the foreach operator which loops through the whole array and works individually with each key/item couple. If a more complex way of traversing the array is needed, the following functions operate using the internal array pointer:

• reset - sets the internal pointer to the first element and returns the first element
• prev - sets the internal pointer to the previous element and returns it
• current - returns the current element; does not change the internal pointer
• next - sets the internal pointer to the next element and returns it
• each - returns the current element; then sets the internal pointer to the next element
• end - sets the internal pointer to the last element and returns the last element

<?php
// using an array's iterator to print its values in reverse order
$my_array = array('a', 'b', 'c');
end($my_array);
while($i = current($my_array)) {
        echo $i."\n";
        prev($my_array);
}
?>

Another possibility is defining a function and applying it to each array element via one of the following functions:

• array_walk - applies a function to each array element
• array_walk_recursive - same, but if the element is itself an array, it will traverse that array too

External Links

• PHP Manual on Arrays
• PHP Manual on Array functions