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Dokumen ini menggunakan Manual laman web PHP Cina Lepaskan
(PHP 4, PHP 5, PHP 7)
array_merge — 合并一个或多个数组
$array1
[, array $...
] )array_merge() 将一个或多个数组的单元合并起来,一个数组中的值附加在前一个数组的后面。返回作为结果的数组。
如果输入的数组中有相同的字符串键名,则该键名后面的值将覆盖前一个值。然而,如果数组包含数字键名,后面的值将不会覆盖原来的值,而是附加到后面。
如果只给了一个数组并且该数组是数字索引的,则键名会以连续方式重新索引。
array1
Initial array to merge.
...
Variable list of arrays to merge.
返回结果数组。
版本 | 说明 |
---|---|
5.0.0 | Warning array_merge() 的行为在 PHP 5 中被修改了。和 PHP 4 不同, array_merge() 现在只接受 array 类型的参数。不过可以用强制转换来合并其它类型。请看下面的例子。
Example #1 array_merge() PHP 5 例子 <?php 以上例程会输出: Array ( [0] => foo [1] => bar ) |
Example #2 array_merge() 例子
<?php
$array1 = array( "color" => "red" , 2 , 4 );
$array2 = array( "a" , "b" , "color" => "green" , "shape" => "trapezoid" , 4 );
$result = array_merge ( $array1 , $array2 );
print_r ( $result );
?>
以上例程会输出:
Array ( [color] => green [0] => 2 [1] => 4 [2] => a [3] => b [shape] => trapezoid [4] => 4 )
Example #3 Simple array_merge() 例子
<?php
$array1 = array();
$array2 = array( 1 => "data" );
$result = array_merge ( $array1 , $array2 );
?>
别忘了数字键名将会被重新编号!
Array ( [0] => data )
如果你想完全保留原有数组并只想新的数组附加到后面,用 + 运算符:
<?php
$array1 = array( 0 => 'zero_a' , 2 => 'two_a' , 3 => 'three_a' );
$array2 = array( 1 => 'one_b' , 3 => 'three_b' , 4 => 'four_b' );
$result = $array1 + $array2 ;
var_dump ( $result );
?>
The keys from the first array will be preserved. If an array key exists in both arrays, then the element from the first array will be used and the matching key's element from the second array will be ignored.
array(5) { [0]=> string(6) "zero_a" [2]=> string(5) "two_a" [3]=> string(7) "three_a" [1]=> string(5) "one_b" [4]=> string(6) "four_b" }
[#1] info at eastghost dot com [2015-09-05 01:37:21]
We noticed array_merge is relatively slower than manually extending an array:
given:
$arr_one[ 'x' => 1, 'y' => 2 ];
$arr_two[ 'a' => 10, 'b' => 20 ];
the statement:
$arr_three = array_merge( $arr_one, $arr_two );
is routinely 200usec slower than:
$arr_three = $arr_one;
foreach( $arr_two as $k => $v ) { $arr_three[ $k ] = $v; }
200usec didn't matter...until we started combining huge arrays.
PHP 5.6.x
[#2] Anonymous [2015-06-29 09:48:04]
As PHP 5.6 you can use array_merge + "splat" operator to reduce a bidimensonal array to a simple array:
<?php
$data = [[1, 2], [3], [4, 5]];
print_r(array_merge(... $data)); // [1, 2, 3, 4, 5];
?>
[#3] gj@php [2014-07-01 14:59:09]
i did a small benchmark (on PHP 5.3.3) comparing:
* using array_merge on numerically indexed arrays
* using a basic double loop to merge multiple arrays
the performance difference is huge:
<?php
require_once("./lib/Timer.php");
function method1($mat){
$all=array();
foreach($mat as $arr){
$all=array_merge($all,$arr);
}
return $all;
}
function method2($mat){
$all=array();
foreach($mat as $arr){
foreach($arr as $el){
$all[]=$el;
}
}
return $all;
}
function tryme(){
$y=250; //#arrays
$x=200; //size per array
$mat=array();
//build big matrix
for($i=0;$i<$y;$i++){
for($j=0;$j<$x;$j++){
$mat[$i][$j]=rand(0,1000);
}
}
$t=new Timer();
method1($mat);
$t->displayTimer();
$t=new Timer();
method2($mat);
$t->displayTimer();
}
tryme();
?>
So that's more than a factor 100!!!!!
[#4] Angel I [2014-06-12 13:57:46]
An addition to what Julian Egelstaff above wrote - the array union operation (+) is not doing an array_unique - it will just not use the keys that are already defined in the left array. The difference between union and merge can be seen in an example like this:
<?php
$arr1['one'] = 'one';
$arr1['two'] = 'two';
$arr2['zero'] = 'zero';
$arr2['one'] = 'three';
$arr2['two'] = 'four';
$arr3 = $arr1 + $arr2;
var_export( $arr3 );
# array ( 'one' => 'one', 'two' => 'two', 'zero' => 'zero', )
$arr4 = array_merge( $arr1, $arr2 );
var_export( $arr4 );
# array ( 'one' => 'three', 'two' => 'four', 'zero' => 'zero', )
?>
[#5] php at metehanarslan dot com [2014-06-10 22:49:49]
Sometimes you need to modify an array with another one here is my approach to replace an array's content recursively with delete opiton. Here i used "::delete::" as reserved word to delete items.
<?php
$person= array(
"name" => "Metehan",
"surname"=>"Arslan",
"age"=>27,
"mail"=>"hidden",
"favs" => array(
"language"=>"php",
"planet"=>"mercury",
"city"=>"istanbul")
);
$newdata = array(
"age"=>28,
"mail"=>"::delete::",
"favs" => array(
"language"=>"js",
"planet"=>"mercury",
"city"=>"shanghai")
);
print_r(array_overlay($person,$newdata));
// result: Array ( [name] => Metehan [surname] => Arslan [age] => 28 [favs] => Array ( [language] => js [planet] => mercury [city] => shanghai ) )
function array_overlay($a1,$a2)
{
foreach($a1 as $k => $v) {
if ($a2[$k]=="::delete::"){
unset($a1[$k]);
continue;
};
if(!array_key_exists($k,$a2)) continue;
if(is_array($v) && is_array($a2[$k])){
$a1[$k] = array_overlay($v,$a2[$k]);
}else{
$a1[$k] = $a2[$k];
}
}
return $a1;
}
?>
[#6] rajaimranqamer at gmail dot com [2014-05-28 08:26:52]
to get unique value from multi dimensional array use this instead of array_unique(), because array_unique() does not work on multidimensional:
array_map("unserialize", array_unique(array_map("serialize", $array)));
Hope this will help someone;
Example
$a=array(array('1'),array('2'),array('3'),array('4));
$b=array(array('2'),array('4'),array('6'),array('8));
$c=array_merge($a,$b);
then write this line to get unique values
$c=array_map("unserialize", array_unique(array_map("serialize", $c)));
print_r($c);
[#7] vladas dot dirzys at gmail dot com [2013-08-21 09:11:06]
To combine several results (arrays):
<?php
$results = array(
array(
array('foo1'),
array('foo2'),
),
array(
array('bar1'),
array('bar2'),
),
);
$rows = call_user_func_array('array_merge', $results);
print_r($rows);
?>
The above example will output:
Array
(
[0] => Array
(
[0] => foo1
)
[1] => Array
(
[0] => foo2
)
[2] => Array
(
[0] => bar1
)
[3] => Array
(
[0] => bar2
)
)
However, example below helps to preserve numeric keys:
<?php
$results = array(
array(
123 => array('foo1'),
456 => array('foo2'),
),
array(
321 => array('bar1'),
654 => array('bar2'),
),
);
$rows = array();
foreach ($results as &$result) {
$rows = $rows + $result; // preserves keys
}
print_r($rows);
?>
The above example will output:
Array
(
[123] => Array
(
[0] => foo1
)
[456] => Array
(
[0] => foo2
)
[321] => Array
(
[0] => bar1
)
[654] => Array
(
[0] => bar2
)
)
[#8] Janez R. [2013-05-16 08:38:10]
Please note that -1 is a numeric key and will be reindexed.
Less obvious numeric keys are also '-1' (becomes -1) and -1.5 (becomes -1).
'-1a', however, is not a numeric key and you could exploit the fact that '-1a' == -1 evaluates to true in php (just a hint). But as this is not very efficient, operator + may be a better option.
<?php
$arr = array(-1=> "-1", '-2'=> "'-2'", -3.5=> "-3.5", '-4a'=> "'-4a'");
print_r(array(
$arr,
array_merge($arr,array()),
'-1a' == -1,
));
?>
Result:
Array
(
[0] => Array
(
[-1] => -1
[-2] => '-2'
[-3] => -3.5
[-4a] => '-4a'
)
[1] => Array
(
[0] => -1
[1] => '-2'
[2] => -3.5
[-4a] => '-4a'
)
[2] => 1
)
[#9] Gemorroj [2012-05-14 08:37:02]
The function behaves differently with numbers more than PHP_INT_MAX
<?php
$arr1 = array('1234567898765432123456789' => 'dd');
$arr2 = array('123456789876543212345678' => 'ddd', '35' => 'xxx');
var_dump(array_merge($arr1, $arr2));
//
$arr1 = array('1234' => 'dd');
$arr2 = array('12345' => 'ddd', '35' => 'xxx');
var_dump(array_merge($arr1, $arr2));
?>
result:
array(3) {
["1234567898765432123456789"]=>
string(2) "dd"
["123456789876543212345678"]=>
string(3) "ddd"
[0]=>
string(3) "xxx"
}
array(3) {
[0]=>
string(2) "dd"
[1]=>
string(3) "ddd"
[2]=>
string(3) "xxx"
}
[#10] izhar_aazmi at gmail dot com [2012-02-28 20:54:52]
The problem that the array keys are reindexed, and further not working on array values of type object or other mixed types.
Simply, I did this:
<?php
foreach($new as $k => $v)
{
$old[$k] = $v;
}
// This will overwrite all values in OLD with any existing
// matching value in NEW
// And keep all non matching values from OLD intact.
// No reindexing, and complete overwrite
/// Working with all kind of data
?>
[#11] alejandro dot anv at gmail dot com [2012-02-20 11:26:31]
WARNING: numeric subindexes are lost when merging arrays.
Check this example:
$a=array('abc'=>'abc','def'=>'def','123'=>'123','xyz'=>'xyz');
echo "a=";print_r($a);
$b=array('xxx'=>'xxx');
echo "b=";print_r($b);
$c=array_merge($a,$b);
echo "c=";print_r($c);
The result is this:
c=Array
(
[abc] => abc
[def] => def
[0] => 123
[xyz] => xyz
[xxx] => xxx
)
[#12] njp AT o2 DOT pl [2011-11-22 04:45:46]
Uniques values merge for array_merge function:
<?php
function array_unique_merge() {
$variables = '$_'.implode(',$_',array_keys(func_get_args()));
$func = create_function('$tab', ' list('.$variables.') = $tab; return array_unique(array_merge('.$variables.'));');
return $func(func_get_args());
}
?>
Doesn't work on objects.
Smarter way for uniques values merge array:
<?php
function array_unique_merge() {
return array_unique(call_user_func_array('array_merge', func_get_args()));
}
?>
Example 1:
$a = array(1,2);
$b = array(2,3,4);
array_unique_merge($a,$b);
Return:
array(1,2,3,4);
Example 2:
$a = array(1,2);
$b = array(2,3,4);
$c = array(2,3,4,5);
array_unique_merge($a,$b);
Return:
array(1,2,3,4,5);
Doesn't work on objects.
[#13] w_barath at hotmail dot com [2011-10-04 16:42:14]
I keep seeing posts for people looking for a function to replace numeric keys.
No function is required for this, it is default behavior if the + operator:
<?php
$a=array(1=>"one", "two"=>2);
$b=array(1=>"two", "two"=>1, 3=>"three", "four"=>4);
print_r($a+$b);
?>
Array
(
[1] => one
[two] => 2
[3] => three
[four] => 4
)
How this works:
The + operator only adds unique keys to the resulting array. By making the replacements the first argument, they naturally always replace the keys from the second argument, numeric or not! =)
[#14] craig ala craigatx.com [2010-10-26 10:25:33]
Reiterating the notes about casting to arrays, be sure to cast if one of the arrays might be null:
<?php
header("Content-type:text/plain");
$a = array('zzzz', 'xxxx');
$b = array('mmmm','nnnn');
echo "1 ==============\r\n";
print_r(array_merge($a, $b));
echo "2 ==============\r\n";
$b = array();
print_r(array_merge($a, $b));
echo "3 ==============\r\n";
$b = null;
print_r(array_merge($a, $b));
echo "4 ==============\r\n";
$b = null;
print_r(array_merge($a, (array)$b));
echo "5 ==============\r\n";
echo is_null(array_merge($a, $b)) ? 'Result is null' : 'Result is not null';
?>
Produces:
1 ==============
Array
(
[0] => zzzz
[1] => xxxx
[2] => mmmm
[3] => nnnn
)
2 ==============
Array
(
[0] => zzzz
[1] => xxxx
)
3 ==============
4 ==============
Array
(
[0] => zzzz
[1] => xxxx
)
5 ==============
Result is null
[#15] nzujev [AT] gmail [DOT] com [2010-10-03 14:28:13]
Be ready to surprise like this one.
array_merge renumbers numeric keys even if key is as string.
keys '1' & '2' will be updated to 0 & 1, but '1.1' & '1.2' remain the same, but they are numeric too (is_numeric('1.1') -> true)
It's better to use '+' operator or to have your own implementation for array_merge.
<?php
$x1 = array (
'1' => 'Value 1',
'1.1' => 'Value 1.1',
);
$x2 = array (
'2' => 'Value 2',
'2.1' => 'Value 2.1',
);
$x3 = array_merge( $x1, $x2 );
echo '<pre>NOT as expected: '. print_r( $x3, true ) .'</pre>';
$x3 = $x1 + $x2;
echo '<pre>As expected: '. print_r( $x3, true ) .'</pre>';
?>
NOT as expected: Array
(
[0] => Value 1
[1.1] => Value 1.1
[1] => Value 2
[2.1] => Value 2.1
)
As expected: Array
(
[1] => Value 1
[1.1] => Value 1.1
[2] => Value 2
[2.1] => Value 2.1
)
[#16] zagadka at evorg dot dk [2010-08-20 05:54:10]
Note that if you use + to merge array in order to preserve keys, that in case of duplicates the values from the left array in the addition is used.
[#17] jpakin at gmail dot com [2010-06-11 11:46:24]
I had a hard time using array_merge with large datasets. By the time my web framework was in memory there wasn't enough space to have multiple copies of my dataset. To fix this I had to remove any functions which operated on the data set and made a copy in memory (pass by value).
I realize the available memory to an application instance is modifiable, but I didn't think I should have to set it below the default 16mb for a web app!
Unfortunately, a number of php functions pass by value internally, so I had to write my own merge function. This passes by reference, utilizes a fast while loop (thus doesn't need to call count() to get an upper boundary, also a php pass by value culprit), and unsets the copy array (freeing memory as it goes).
<?php
function mergeArrays(&$sourceArray, &$copyArray){
//merge copy array into source array
$i = 0;
while (isset($copyArray[$i])){
$sourceArray[] = $copyArray[$i];
unset($copyArray[$i]);
$i++;
}
}
?>
This fixed the problem. I would love to know if there is an even faster, more efficient way. Simply adding the two arrays won't work since there is an overlap of index.
[#18] nekroshorume at gmail dot com [2010-03-18 10:31:40]
be aware there is a slight difference:
<?php
$array1 = array('lang'=>'js','method'=>'GET');
$array2 = array('lang'=>'php','browser'=>'opera','method'=>'POST');
?>
BETWEEN:
<?php array_merge($array2,$array1); ?>
outputs: Array ( [lang] => js [browser] => opera [method] => GET )
notice that the repeated keys will be overwritten by the ones of $array1, maintaining those, because it is the array that is being merged
AND
<?php array_merge($array1,$array2); ?>
outputs: Array ( [lang] => php [method] => POST [browser] => opera )
here the oposite takes place: array1 will have its elements replaced by those of array2.
[#19] riddlemd at gmail dot com [2010-01-22 00:43:14]
Apparently there is a shorthand that works very much like array_merge. I figured I would leave a comment here, sense I saw it used in code but found nothing about it from google searches.
<?php
$array = array(
'name' => 'John Doe'
);
$array += array(
'address' => 'someplace somestreet'
);
echo $array['address']; // Outputs 'someplace somestreet'
?>
A difference from merge_array, it does NOT overwrite existing keys, regardless of key type.
[#20] allankelly [2009-10-02 08:36:04]
More on the union (+) operator:
the order of arrays is important and does not agree in my test below
with the other posts. The 'unique' operation preserves the initial key-value and discards later duplicates.
PHP 5.2.6-2ubuntu4.2
<?php
$a1=array('12345'=>'a', '23456'=>'b', '34567'=>'c', '45678'=>'d');
$a2=array('34567'=>'X');
$a3=$a1 + $a2;
$a4=$a2 + $a1;
print('a1:'); print_r($a1);
print('a2:'); print_r($a2);
print('a3:'); print_r($a3);
print('a4:'); print_r($a4);
?>
a1:Array
(
[12345] => a
[23456] => b
[34567] => c
[45678] => d
)
a2:Array
(
[34567] => X
)
a3:Array
(
[12345] => a
[23456] => b
[34567] => c
[45678] => d
)
a4:Array
(
[34567] => X
[12345] => a
[23456] => b
[45678] => d
)
[#21] Tudor [2009-09-27 13:10:15]
array_merge will merge numeric keys in array iteration order, not in increasing numeric order. For example:
<?php
$a = array(0=>10, 1=>20); // same as array(10, 20);
$b = array(0=>30, 2=>50, 1=>40);
?>
array_merge($a, $b) will be array(10, 20, 30, 50, 40) and not array(10, 20, 30, 40, 50).
[#22] Julian Egelstaff [2009-08-16 13:02:19]
More about the union operator (+)...
The "array_unique" that gets applied, is actually based on the keys, not the values. So if you have multiple values with the same key, only the last one will be preserved.
<?php
$array1[0] = "zero";
$array1[1] = "one";
$array2[0] = 0;
$array1[1] = 1;
$array3 = $array1 + $array2;
// array3 will look like:
// array(0=>0, 1=>1)
// ie: beware of the latter keys overwriting the former keys
?>
[#23] Julian Egelstaff [2009-07-30 23:48:54]
In some situations, the union operator ( + ) might be more useful to you than array_merge. The array_merge function does not preserve numeric key values. If you need to preserve the numeric keys, then using + will do that.
ie:
<?php
$array1[0] = "zero";
$array1[1] = "one";
$array2[1] = "one";
$array2[2] = "two";
$array2[3] = "three";
$array3 = $array1 + $array2;
//This will result in::
$array3 = array(0=>"zero", 1=>"one", 2=>"two", 3=>"three");
?>
Note the implicit "array_unique" that gets applied as well. In some situations where your numeric keys matter, this behaviour could be useful, and better than array_merge.
--Julian
[#24] enaeseth at gmail dot com [2009-07-20 14:27:16]
In both PHP 4 and 5, array_merge preserves references in array values. For example:
<?php
$foo = 12;
$array = array("foo" => &$foo);
$merged_array = array_merge($array, array("bar" => "baz"));
$merged_array["foo"] = 24;
assert($foo === 24); // works just fine
?>
[#25] jerry at gii dot co dot jp [2009-03-12 07:35:57]
There was a previous note that alluded to this, but at least in version 5.2.4 array_merge will return NULL if any of the arguments are NULL. This bit me with $_POST when none of the controls were successful.
[#26] carrox at inbox dot lv [2008-08-31 16:41:21]
Usage of operand '+' for merging arrays:
<?php
$a=array(
'a'=>'a1',
'b'=>'a2',
'a3',
'a4',
'a5');
$b=array('b1',
'b2',
'a'=>'b3',
'b4');
$a+=$b;
print_r($a);
?>
output:
Array
(
[a] => a1
[b] => a2
[0] => a3
[1] => a4
[2] => a5
[3] => b5
)
numeric keys of elements of array B what not presented in array A was added.
<?php
$a=array('a'=>'a1','b'=>'a2','a3','a4','a5');
$b=array(100=>'b1','b2','a'=>'b3','b4');
$a+=$b;
print_r($a);
?>
output:
[a] => a1
[b] => a2
[0] => a3
[1] => a4
[2] => a5
[100] => b1
[101] => b2
[102] => b4
autoindex for array B started from 100, these keys not present in array A, so this elements was added to array A
[#27] ron at ronfolio dot com [2008-08-11 18:44:06]
I needed a function similar to ian at fuzzygroove's array_interlace, but I need to pass more than two arrays.
Here's my version, You can pass any number of arrays and it will interlace and key them properly.
<?php
function array_interlace() {
$args = func_get_args();
$total = count($args);
if($total < 2) {
return FALSE;
}
$i = 0;
$j = 0;
$arr = array();
foreach($args as $arg) {
foreach($arg as $v) {
$arr[$j] = $v;
$j += $total;
}
$i++;
$j = $i;
}
ksort($arr);
return array_values($arr);
}
?>
Example usage:
<?php
$a = array('a', 'b', 'c', 'd');
$b = array('e', 'f', 'g');
$c = array('h', 'i', 'j');
$d = array('k', 'l', 'm', 'n', 'o');
print_r(array_interlace($a, $b, $c, $d));
?>
result:
Array
(
[0] => a
[1] => e
[2] => h
[3] => k
[4] => b
[5] => f
[6] => i
[7] => l
[8] => c
[9] => g
[10] => j
[11] => m
[12] => d
[13] => n
[14] => o
)
Let me know if you improve on it.
[#28] david_douard at hotmail dot com [2008-07-02 02:41:23]
To avoid REINDEXING issues,
use + operator :
array_merge(
array("truc" => "salut"),
array("machin" => "coucou")
)
returns
array(2)
{
[0] => string() "salut"
[1] => string() "coucou"
}
whereas
array("truc" => "salut") + array("machin" => "coucou")
returns
array(2)
{
["truc"] => string() "salut"
["machin"] => string() "coucou"
}
[#29] bishop [2008-04-04 14:02:26]
The documentation is a touch misleading when it says: "If only one array is given and the array is numerically indexed, the keys get reindexed in a continuous way." Even with two arrays, the resulting array is re-indexed:
[bishop@predator staging]$ cat array_merge.php
<?php
$a = array (23 => 'Hello', '42' => 'World');
$a = array_merge(array (0 => 'I say, '), $a);
var_dump($a);
?>
[bishop@predator staging]$ php-5.2.5 array_merge.php
array(3) {
[0]=>
string(7) "I say, "
[1]=>
string(5) "Hello"
[2]=>
string(5) "World"
}
[bishop@predator staging]$ php-4.4.7 array_merge.php
array(3) {
[0]=>
string(7) "I say, "
[1]=>
string(5) "Hello"
[2]=>
string(5) "World"
}
[#30] no_one at nobody dot com [2008-03-03 08:31:43]
PHP is wonderfully decides if an array key could be a number, it is a number! And thus wipes out the key when you array merge. Just a warning.
$array1['4000'] = 'Grade 1 Widgets';
$array1['4000a'] = 'Grade A Widgets';
$array2['5830'] = 'Grade 1 Thing-a-jigs';
$array2['HW39393'] = 'Some other widget';
var_dump($array1);
var_dump($array2);
//results in...
array(2) {
[4000]=>
string(15) "Grade 1 Widgets"
["4000a"]=>
string(15) "Grade A Widgets"
}
array(2) {
[5830]=>
string(20) "Grade 1 Thing-a-jigs"
["HW39393"]=>
string(17) "Some other widget"
}
var_dump(array_merge($array1,$array2));
//results in...
array(4) {
[0]=>
string(15) "Grade 1 Widgets"
["4000a"]=>
string(15) "Grade A Widgets"
[1]=>
string(20) "Grade 1 Thing-a-jigs"
["HW39393"]=>
string(17) "Some other widget"
}
[#31] Hayley Watson [2007-11-04 12:38:37]
As has already been noted before, reindexing arrays is most cleanly performed by the array_values() function.
[#32] clancyhood at gmail dot com [2007-07-21 16:52:54]
Similar to Jo I had a problem merging arrays (thanks for that Jo you kicked me out of my debugging slumber) - array_merge does NOT act like array_push, as I had anticipated
<?php
$array = array('1', 'hello');
array_push($array, 'world');
var_dump($array);
// gives '1', 'hello', 'world'
$array = array('1', 'hello');
array_merge($array, array('world'));
// gives '1', 'hello'
$array = array('1', 'hello');
$array = array_merge($array, array('world'));
// gives '1', 'hello', 'world'
?>
hope this helps someone
[#33] Joe at neosource dot com dot au [2007-06-03 23:51:18]
I found the "simple" method of adding arrays behaves differently as described in the documentation in PHP v5.2.0-10.
$array1 + $array2 will only combine entries for keys that don't already exist.
Take the following example:
$ar1 = array('a', 'b');
$ar2 = array('c', 'd');
$ar3 = ($ar1 + $ar2);
print_r($ar3);
Result:
Array
(
[0] => a
[1] => b
)
Where as:
$ar1 = array('a', 'b');
$ar2 = array('c', 'd');
$ar3 = array_merge($ar1, $ar2);
print_r($ar3);
Result:
Array
(
[0] => a
[1] => b
[2] => c
[3] => d
)
Hope this helps someone.
[#34] RQuadling at GMail dot com [2007-05-21 05:05:00]
For asteddy at tin dot it and others who are trying to merge arrays and keep the keys, don't forget the simple + operator.
Using the array_merge_keys() function (with a small mod to deal with multiple arguments), provides no difference in output as compared to +.
<?php
$a = array(-1 => 'minus 1');
$b = array(0 => 'nought');
$c = array(0 => 'nought');
var_export(array_merge_keys($a,$b));
var_export($a + $b);
var_export(array_merge_keys($a,$b,$c));
var_export($a + $b + $c);
?>
results in ...
array ( -1 => 'minus 1', 0 => 'nought',)
array ( -1 => 'minus 1', 0 => 'nought',)
array ( -1 => 'minus 1', 0 => 'nought',)
array ( -1 => 'minus 1', 0 => 'nought',)
[#35] Marce! [2007-03-02 04:21:36]
I have been searching for an in-place merge function, but couldn't find one. This function merges two arrays, but leaves the order untouched.
Here it is for all others that want it:
function inplacemerge($a, $b) {
$result = array();
$i = $j = 0;
if (count($a)==0) { return $b; }
if (count($b)==0) { return $a; }
while($i < count($a) && $j < count($b)){
if ($a[$i] <= $b[$j]) {
$result[] = $a[$i];
if ($a[$i]==$b[$j]) { $j++; }
$i++;
} else {
$result[] = $b[$j];
$j++;
}
}
while ($i<count($a)){
$result[] = $a[$i];
$i++;
}
while ($j<count($b)){
$result[] = $b[$j];
$j++;
}
return $result;
}
[#36] ahigerd at stratitec dot com [2007-01-24 06:06:21]
An earlier comment mentioned that array_splice is faster than array_merge for inserting values. This may be the case, but if your goal is instead to reindex a numeric array, array_values() is the function of choice. Performing the following functions in a 100,000-iteration loop gave me the following times: ($b is a 3-element array)
array_splice($b, count($b)) => 0.410652
$b = array_splice($b, 0) => 0.272513
array_splice($b, 3) => 0.26529
$b = array_merge($b) => 0.233582
$b = array_values($b) => 0.151298
[#37] zspencer at zacharyspencer dot com [2006-11-09 08:55:56]
I noticed the lack of a function that will safely merge two arrays without losing data due to duplicate keys but different values.
So I wrote a quicky that would offset duplicate keys and thus preserve their data. of course, this does somewhat mess up association...
<?php
$array1=array('cats'=>'Murder the beasties!', 'ninjas'=>'Use Ninjas to murder cats!');
$array2=array('cats'=>'Cats are fluffy! Hooray for Cats!', 'ninjas'=>'Ninas are mean cat brutalizers!!!');
$array3=safe_array_merge($array1, $array2);
print_r($array3)
function array_deep_merge()
{
switch( func_num_args() )
{
case 0 : return false; break;
case 1 : return func_get_arg(0); break;
case 2 :
$args = func_get_args();
$args[2] = array();
if( is_array($args[0]) and is_array($args[1]) )
{
foreach( array_unique(array_merge(array_keys($args[0]),array_keys($args[1]))) as $key )
if( is_string($key) and is_array($args[0][$key]) and is_array($args[1][$key]) )
$args[2][$key] = array_deep_merge( $args[0][$key], $args[1][$key] );
elseif( is_string($key) and isset($args[0][$key]) and isset($args[1][$key]) )
$args[2][$key] = $args[1][$key];
elseif( is_integer($key) and isset($args[0][$key]) and isset($args[1][$key]) ) {
$args[2][] = $args[0][$key]; $args[2][] = $args[1][$key]; }
elseif( is_integer($key) and isset($args[0][$key]) )
$args[2][] = $args[0][$key];
elseif( is_integer($key) and isset($args[1][$key]) )
$args[2][] = $args[1][$key];
elseif( ! isset($args[1][$key]) )
$args[2][$key] = $args[0][$key];
elseif( ! isset($args[0][$key]) )
$args[2][$key] = $args[1][$key];
return $args[2];
}
else return $args[1]; break;
default :
$args = func_get_args();
$args[1] = array_deep_merge( $args[0], $args[1] );
array_shift( $args );
return call_user_func_array( 'array_deep_merge', $args );
break;
}
}
$a = array(
0,
array( 0 ),
'integer' => 123,
'integer456_merge_with_integer444' => 456,
'integer789_merge_with_array777' => 789,
'array' => array( "string1", "string2" ),
'array45_merge_with_array6789' => array( "string4", "string5" ),
'arraykeyabc_merge_with_arraykeycd' => array( 'a' => "a", 'b' => "b", 'c' => "c" ),
'array0_merge_with_integer3' => array( 0 ),
'multiple_merge' => array( 1 ),
);
$b = array(
'integer456_merge_with_integer444' => 444,
'integer789_merge_with_array777' => array( 7,7,7 ),
'array45_merge_with_array6789' => array( "string6", "string7", "string8", "string9" ),
'arraykeyabc_merge_with_arraykeycd' => array( 'c' => "ccc", 'd' => "ddd" ),
'array0_merge_with_integer3' => 3,
'multiple_merge' => array( 2 ),
);
$c = array(
'multiple_merge' => array( 3 ),
);
echo "<pre>".htmlentities(print_r( array_deep_merge( $a, $b, $c ), true))."</pre>";
?>
[#47] ntpt at centrum dot cz [2005-07-14 06:44:00]
Old behavior of array_merge can be restored by simple variable type casting like this
array_merge((array)$foo,(array)$bar);
works good in php 5.1.0 Beta 1, not tested in other versions
seems that empty or not set variables are casted to empty arrays
[#48] Alec Solway [2005-01-20 10:05:58]
Note that if you put a number as a key in an array, it is eventually converted to an int even if you cast it to a string or put it in quotes.
That is:
$arr["0"] = "Test";
var_dump( key($arr) );
will output int(0).
This is important to note when merging because array_merge will append values with a clashing int-based index instead of replacing them. This kept me tied up for hours.
[#49] nospam at veganismus dot ch [2005-01-11 06:38:17]
Someone posted a function with the note:
"if u need to overlay a array that holds defaultvalues with another that keeps the relevant data"
<?php
//about twice as fast but the result is the same.
//note: the sorting will be messed up!
function array_overlay($skel, $arr) {
return $arr+$skel;
}
//example:
$a = array("zero","one","two");
$a = array_overlay($a,array(1=>"alpha",2=>NULL));
var_dump($a);
?>
[#50] Frederick.Lemasson{AT}kik-it.com [2004-12-23 02:57:40]
if you generate form select from an array, you probably want to keep your array keys and order intact,
if so you can use ArrayMergeKeepKeys(), works just like array_merge :
array ArrayMergeKeepKeys ( array array1 [, array array2 [, array ...]])
but keeps the keys even if of numeric kind.
enjoy
<?php
$Default[0]='Select Something please';
$Data[147]='potato';
$Data[258]='banana';
$Data[54]='tomato';
$A=array_merge($Default,$Data);
$B=ArrayMergeKeepKeys($Default,$Data);
echo '<pre>';
print_r($A);
print_r($B);
echo '</pre>';
Function ArrayMergeKeepKeys() {
$arg_list = func_get_args();
foreach((array)$arg_list as $arg){
foreach((array)$arg as $K => $V){
$Zoo[$K]=$V;
}
}
return $Zoo;
}
//will output :
Array
(
[0] => Select Something please
[1] => potato
[2] => banana
[3] => tomato
)
Array
(
[0] => Select Something please
[147] => potato
[258] => banana
[54] => tomato
)
?>
[#51] bcraigie at bigfoot dot com [2004-08-24 12:37:59]
It would seem that array_merge doesn't do anything when one array is empty (unset):
<?php //$a is unset
$b = array("1" => "x");
$a = array_merge($a, $b});
//$a is still unset.
?>
to fix this omit $a if it is unset:-
<?php
if(!IsSet($a)) {
$a = array_merge($b);
} else {
$a = array_merge($a, $b);
}
?>
I don't know if there's a better way.
[#52] frankb at fbis dot net [2004-02-25 04:02:22]
to merge arrays and preserve the key i found the following working with php 4.3.1:
<?php
$array1 = array(1 => "Test1", 2 => "Test2");
$array2 = array(3 => "Test3", 4 => "Test4");
$array1 += $array2;
?>
dont know if this is working with other php versions but it is a simple and fast way to solve that problem.
[#53] rcarvalhoREMOVECAPS at clix dot pt [2003-11-03 12:43:24]
While searching for a function that would renumber the keys in a array, I found out that array_merge() does this if the second parameter is null:
Starting with array $a like:
<?php
Array
(
[5] => 5
[4] => 4
[2] => 2
[9] => 9
)
?>
Then use array_merge() like this:
<?php
$a = array_merge($a, null);
?>
Now the $a array has bee renumbered, but maintaining the order:
<?php
Array
(
[0] => 5
[1] => 4
[2] => 2
[3] => 9
)
?>
Hope this helps someone :-)
[#54] loner at psknet dot !NOSPAM!com [2003-09-29 15:00:35]
I got tripped up for a few days when I tried to merge a (previously serialized) array into a object. If it doesn't make sense, think about it... To someone fairly new, it could... Anyway, here is what I did:
(It's obviously not recursive, but easy to make that way)
<?php
function array_object_merge(&$object, $array) {
foreach ($array as $key => $value)
$object->{$key} = $value;
}
?>
Simple problem, but concevibly easy to get stuck on.
[#55] [2003-09-03 15:10:54]
For those who are getting duplicate entries when using this function, there is a very easy solution:
wrap array_unique() around array_merge()
cheers,
k.
[#56] tobias_mik at hotmail dot com [2003-07-25 05:14:02]
This function merges any number of arrays and maintains the keys:
<?php
function array_kmerge ($array) {
reset($array);
while ($tmp = each($array))
{
if(count($tmp['value']) > 0)
{
$k[$tmp['key']] = array_keys($tmp['value']);
$v[$tmp['key']] = array_values($tmp['value']);
}
}
while($tmp = each($k))
{
for ($i = $start; $i < $start+count($tmp['value']); $i ++)$r[$tmp['value'][$i-$start]] = $v[$tmp['key']][$i-$start];
$start = count($tmp['value']);
}
return $r;
}
?>