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
)
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);
?>
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)
?>
add a note
User Contributed Notes 7 notes
cb at netalyst dot com ¶
16 years ago
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",
}
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)
?>
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
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.
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.
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 )
