数组运算符

数组运算符
例子 名称 结果
$a + $b 联合 $a 和 $b 的联合。
$a == $b 相等 如果 $a 和 $b 具有相同的键／值对则为 true。
$a === $b 全等 如果 $a 和 $b 具有相同的键／值对并且顺序和类型都相同则为 true。
$a != $b 不等 如果 $a 不等于 $b 则为 true。
$a <> $b 不等 如果 $a 不等于 $b 则为 true。
$a !== $b 不全等 如果 $a 不全等于 $b 则为 true。

+ 运算符把右边的数组元素附加到左边的数组后面，两个数组中都有的键名，则只用左边数组中的，右边的被忽略。

<?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);
?>
执行后，此脚本会显示： 
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"
}

数组中的单元如果具有相同的键名和值则比较时相等。

Example #1 比较数组

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

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

参见

User Contributed Notes

drone dot ah at gmail dot com 06-Oct-2017 09:51
The note about array comparison by Q1712 is not entirely accurate.

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

This may have been the case in past (I cannot verify it). It requires that the keys are in the same order AND that the values match

To extend that example

<?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)

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

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

?>
xtpeqii at Hotmail dot com 21-Sep-2017 08:02
$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.
Anonymous 29-Jan-2014 12:23
The manual say ...

"The + operator appends the right elements in the array from left, whereas duplicated keys are NOT overwritten"

but ..

$a = array("a" => 'A', "b" => 'B');
$b = array("a" => 'A', "b" => 'B', "c" => 'C');

$c = $a + $b // or $b + a  is  the same output;

echo '<pre>';

print_r($c);

echo '<pre>';

//Output   for  $a + b  or  $b + a
Array (
    [a] => A
    [b] => B
    [c] => C
)
sd6733531 at gmail dot com 30-Mar-2013 07:18
Look out use + with array combine.

$arr = array(1, 2, 3);
$int=345;
$arr=$arr+$int;

Of couse,use + to combine array is easy and readable.
But if one of the variable is not array type(like above code) ,that would make a PHP Fatal Error:
PHP Fatal error:  Unsupported operand types
Maybe should do check before.
Dan Patrick 04-Mar-2012 06:39
It should be mentioned that the array union operator functions almost identically to array_replace with the exception that precedence of arguments is reversed.
cb at netalyst dot com 15-Oct-2008 11:39
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
)
csaba at alum dot mit dot edu 24-Jun-2008 08:54
Simple array arithmetic:
A more compact way of adding or subtracting the elements at identical keys...

<?php
function array_add($a1, $a2) {  // ...
  // adds the values at identical keys together
  $aRes = $a1;
  foreach (array_slice(func_get_args(), 1) as $aRay) {
    foreach (array_intersect_key($aRay, $aRes) as $key => $val) $aRes[$key] += $val;
    $aRes += $aRay; }
  return $aRes; }

function array_subtract($a1, $a2) {  // ...
  // adds the values at identical keys together
  $aRes = $a1;
  foreach (array_slice(func_get_args(), 1) as $aRay) {
    foreach (array_intersect_key($aRay, $aRes) as $key => $val) $aRes[$key] -= $val;
    foreach (array_diff_key($aRay, $aRes) as $key => $val) $aRes[$key] = -$val; }
  return $aRes; }

Example:
$a1 = array(9, 8, 7);
$a2 = array(1=>7, 6, 5);
$a3 = array(2=>5, 4, 3);

$aSum = array_add($a1, $a2, $a3);
$aDiff = array_subtract($a1, $a2, $a3);

// $aSum  => [9, 15, 18, 9, 3]
// $aDiff => [9, 1, -4, -9, -3]
?>

To make a similar function, array_concatenate(), change only the first of the two '+=' in array_add() to '.='
Csaba Gabor from Vienna
Q1712 at online dot ms 20-Apr-2007 05:54
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)
?>
puneet singh @ value-one dot com 18-Jan-2006 10:42
hi  just see one more example of union....

<?php
$a = array(1,2,3);
$b = array(1,7,8,9,10);
$c = $a + $b; // Union of $a and $b
echo "Union of \$a and \$b: \n";
//echo $c
print_r($c);
?>
//output
Union of $a and $b: Array ( [0] => 1 [1] => 2 [2] => 3 [3] => 9 [4] => 10 )
kit dot lester at lycos dot co dot uk 21-Aug-2005 09:01
When comparing arrays that have (some or all) element-values that are themselves array, then in PHP5 it seems that == and === are applied recursively - that is
 * two arrays satisfy == if they have the same keys, and the values at each key satisfy == for whatever they happen to be (which might be arrays);
 * two arrays satisfy === if they have the same keys, and the values at each key satisfy === for whatever (etc.).

Which explains what happens if we compare two arrays of arrays of arrays of...

Likewise, the corresponding inversions for != <> and !==.

I've tested this to array-of-array-of-array, which seems fairly convincing. I've not tried it in PHP4 or earlier.
kit dot lester at lycos dot co dot uk 21-Aug-2005 08:44
This manual page doesn't mention < & co for arrays, but example 15-2 in
    http://www.php.net/manual/en/language.operators.comparison.php
goes to some lengths to explain how they work.
dfranklin at fen dot com 22-Apr-2004 01:40
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
amirlaher AT yahoo DOT co SPOT uk 09-Dec-2002 10:41
[]= 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 )
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