PHP: Hypertext Preprocessor

Array Operators

**Array Operators**
Example	Name	Result
$a + $b	Union	Union of `$a` and `$b`.
$a == $b	Equality	`true` if `$a` and `$b` have the same key/value pairs.
$a === $b	Identity	`true` if `$a` and `$b` have the same key/value pairs in the same order and of the same types.
$a != $b	Inequality	`true` if `$a` is not equal to `$b`.
$a <> $b	Inequality	`true` if `$a` is not equal to `$b`.
$a !== $b	Non-identity	`true` if `$a` is not identical to `$b`.

The + operator returns the right-hand array appended to the left-hand array; for keys that exist in both arrays, the elements from the left-hand array will be used, and the matching elements from the right-hand array will be ignored.

<?php
$a = array("a" => "apple", "b" => "banana");
$b = array("a" => "pear", "b" => "strawberry", "c" => "cherry");

$c = $a + $b; // Union of $a and $b
echo "Union of \$a and \$b: \n";
var_dump($c);

$c = $b + $a; // Union of $b and $a
echo "Union of \$b and \$a: \n";
var_dump($c);

$a += $b; // Union of $a += $b is $a and $b
echo "Union of \$a += \$b: \n";
var_dump($a);
?>

When executed, this script will print the following:

Union of $a and $b:
array(3) {
  ["a"]=>
  string(5) "apple"
  ["b"]=>
  string(6) "banana"
  ["c"]=>
  string(6) "cherry"
}
Union of $b and $a:
array(3) {
  ["a"]=>
  string(4) "pear"
  ["b"]=>
  string(10) "strawberry"
  ["c"]=>
  string(6) "cherry"
}
Union of $a += $b:
array(3) {
  ["a"]=>
  string(5) "apple"
  ["b"]=>
  string(6) "banana"
  ["c"]=>
  string(6) "cherry"
}

Elements of arrays are equal for the comparison if they have the same key and value.

Example #1 Comparing arrays

<?php
$a = array("apple", "banana");
$b = array(1 => "banana", "0" => "apple");

var_dump($a == $b); // bool(true)
var_dump($a === $b); // bool(false)
?>

Improve This Page

Learn How To Improve This Page • Submit a Pull Request • Report a Bug

＋add a note

User Contributed Notes 7 notes

down

238

cb at netalyst dot com ¶

16 years ago

The union operator did not behave as I thought it would on first glance. It implements a union (of sorts) based on the keys of the array, not on the values.

For instance:
<?php
$a = array('one','two');
$b=array('three','four','five');

//not a union of arrays' values
echo '$a + $b : ';
print_r ($a + $b);

//a union of arrays' values
echo "array_unique(array_merge($a,$b)):";
// cribbed from http://oreilly.com/catalog/progphp/chapter/ch05.html
print_r (array_unique(array_merge($a,$b)));
?>

//output

$a + $b : Array
(
    [0] => one
    [1] => two
    [2] => five
)
array_unique(array_merge(Array,Array)):Array
(
    [0] => one
    [1] => two
    [2] => three
    [3] => four
    [4] => five
)

down

Q1712 at online dot ms ¶

17 years ago

The example may get u into thinking that the identical operator returns true because the key of apple is a string but that is not the case, cause if a string array key is the standart representation of a integer it's gets a numeral key automaticly. 

The identical operator just requires that the keys are in the same order in both arrays:

<?php
$a = array (0 => "apple", 1 => "banana");
$b = array (1 => "banana", 0 => "apple");

var_dump($a === $b); // prints bool(false) as well

$b = array ("0" => "apple", "1" => "banana");

var_dump($a === $b); // prints bool(true)
?>

down

dfranklin at fen dot com ¶

20 years ago

Note that + will not renumber numeric array keys.  If you have two numeric arrays, and their indices overlap, + will use the first array's values for each numeric key, adding the 2nd array's values only where the first doesn't already have a value for that index.  Example:

$a = array('red', 'orange');
$b = array('yellow', 'green', 'blue');
$both = $a + $b;
var_dump($both);

Produces the output:

array(3) { [0]=>  string(3) "red" [1]=>  string(6) "orange" [2]=>  string(4) "blue" }

To get a 5-element array, use array_merge.

    Dan

down

xtpeqii at Hotmail dot com ¶

7 years ago

$a=[ 3, 2, 1];
$b=[ 6, 5, 4];
var_dump( $a + $b );

output:
array(3) {
  [0]=>
  int(3)
  [1]=>
  int(2)
  [2]=>
  int(1)
}

The reason for the above output is that EVERY array in PHP is an associative one.  
Since the 3 elements in $b have the same keys( or numeric indices ) as those in $a, those elements in $b are ignored by the union operator.

down

amirlaher AT yahoo DOT co SPOT uk ¶

21 years ago

[]= could be considered an Array Operator (in the same way that .= is a String Operator). 
[]= pushes an element onto the end of an array, similar to array_push:
<? 
  $array= array(0=>"Amir",1=>"needs");
  $array[]= "job";
  print_r($array);
?>
Prints: Array ( [0] => Amir [1] => needs [2] => job )

down

Dan Patrick ¶

12 years ago

It should be mentioned that the array union operator functions almost identically to array_replace with the exception that precedence of arguments is reversed.

down

Anonymous ¶

2 years ago

Merge two arrays and retain only unique values.
Append values from second array.
Do not care about keys.

<?php
$array1 = [
    0 => 'apple',
    1 => 'orange',
    2 => 'pear',
];

$array2 = [
    0 => 'melon',
    1 => 'orange',
    2 => 'banana',
];

$result = array_keys(
    array_flip($array1) + array_flip($array2)
);
?>

Result:
[
  [0] => "apple",
  [1] => "orange",
  [2] => "pear",
  [3] => "melon",
  [4] => "banana",
}

＋add a note

Array Operators

See Also

Improve This Page

User Contributed Notes 7 notes