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
)
PHP - Manual: 数组运算符
2024-11-14
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; // $a 和 $b 的并集
echo "Union of \$a and \$b: \n";
var_dump($c);
$c = $b + $a; // $b 和 $a 的并集
echo "Union of \$b and \$a: \n";
var_dump($c);
$a += $b; // $a += $b 的并集是 $a 和 $b
echo "Union of \$a += \$b: \n";
var_dump($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"
}
数组中的单元如果具有相同的键名和值则比较时相等。
示例 #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)
?>
add a note
User Contributed Notes 13 notes
cb at netalyst dot com ¶
13 years ago
Q1712 at online dot ms ¶
15 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)
?>
Dan Patrick ¶
10 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.
dfranklin at fen dot com ¶
18 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
drone dot ah at gmail dot com ¶
4 years ago
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)
?>
amirlaher AT yahoo DOT co SPOT uk ¶
19 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 )
xtpeqii at Hotmail dot com ¶
4 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 $b are ignored by the union operator.
csaba at alum dot mit dot edu ¶
13 years ago
Simple array arithmetic:
A more compact way of adding or subtracting the elements at identical keys...
<?php
function array_add($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
kit dot lester at lycos dot co dot uk ¶
16 years ago
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 ¶
16 years ago
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.
puneet singh @ value-one dot com ¶
16 years ago
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 )
sd6733531 at gmail dot com ¶
9 years ago
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.
Anonymous ¶
8 years ago
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
)
官方地址：https://www.php.net/manual/en/language.operators.array.php
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