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PHP Programming/Arrays
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Arrays are sets of data that 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 up the array 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
$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);
?> 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
) 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
echo "Manufacturer: {$array['name']} \n";
echo "Brand: <b>{$array2['1']}</b><br />\n";
echo "Colour: <b>".$array3['colour']."</b><br />\n";
echo "Year Manufactured: <b>".$array3[1]."</b><br />\n"
?> Manufacturer: <b>Toyota</b><br />
Brand: <b>Celica</b><br />
Colour: <b>black</b><br />
Year Manufactured: <b>1991</b><br /> 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).
Sorting
Examples:
$array = array("name"=>"Toyota", "type"=>"Celica", "colour"=>"black", "manufactured"=>"1991");
array_multisort($array, SORT_ASC);
var_dump($array);
// array(4) { ["manufactured"]=> string(4) "1991" ["type"]=> string(6) "Celica" ["name"]=> string(6) "Toyota" ["colour"]=> string(5) "black" }
// The upper cases are sorted before the lowercases.
arsort($array);
var_dump($array);
// array(4) { ["colour"]=> string(5) "black" ["name"]=> string(6) "Toyota" ["type"]=> string(6) "Celica" ["manufactured"]=> string(4) "1991" }
asort($array);
var_dump($array);
// array(4) { ["manufactured"]=> string(4) "1991" ["type"]=> string(6) "Celica" ["name"]=> string(6) "Toyota" ["colour"]=> string(5) "black" }
sort($array);
var_dump($array);
// array(4) { [0]=> string(4) "1991" [1]=> string(6) "Celica" [2]=> string(6) "Toyota" [3]=> string(5) "black" }
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 that 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 Array functions
PHP Manual on Arrays