array_merge與 +

<?php
$arr1 = array('a'=>'PHP');
$arr2 = array('a'=>'PYTHON');
print_r(array_merge($arr1,$arr2)); //Array ( [a] => PYTHON ) 如果鍵名爲字符，且鍵名相同，array_merge()後面數組元素值會覆蓋前面數組元素值
print_r($arr1+$arr2); //Array ( [a] => PHP )如果鍵名爲字符，且鍵名相同，數組相加會將最先出現的值作爲結果

//再比如

$arr1 = array('a'=>'1','b'=>'2');
$arr2 = array('a'=>'1','b'=>'3','c'=>'2');
$ret = array_merge($arr1,$arr2);
print_r($ret);//Array ( [a] => 1 [b] => 3 [c] => 2 )

$ret = $arr1+$arr2;
print_r($ret);//Array ( [a] => 1 [b] => 2 [c] => 2 )

<?php
$arr1 = array("JAVA","PHP");
$arr2 = array("PYTHON","PHP");
print_r(array_merge($arr1,$arr2));//Array ( [0] => JAVA [1] => PHP [2] => PYTHON [3] => PHP ) 如果鍵名爲數字，array_merge()不會進行覆蓋
print_r($arr1+$arr2);//Array ( [0] => JAVA [1] => PHP )如果鍵名爲數字，數組相加會將最先出現的值作爲結果，後面鍵名相同的會被拋棄

//再比如

$arr1 = array(1=>'1',2=>'2');
$arr2 = array(1=>'1',2=>'3',8=>'2');

$ret = array_merge($arr1,$arr2);
print_r($ret);//Array ( [0] => 1 [1] => 2 [2] => 1 [3] => 3 [4] => 2 ) 如果數組中的鍵名爲數字時，會格式化鍵名並保留所有鍵值。

//再比如

$arr1 = array(1,2);
$arr2 = array(1,2,8);

$ret = array_merge($arr1,$arr2);
print_r($ret);//Array ( [0] => 1 [1] => 2 [2] => 1 [3] => 2 [4] => 8 )

?>

 

特別要注意。關於“array_merge和數組相加的區別”上面已經闡述的很清楚了，“如何最有效的獲取字符鍵名相同值不同的兩個數組值集合呢”，不會這要對每個數組遍歷吧，PHP中還有一個函數：array_merge_recursive

— 遞歸地合併一個或多個數組，如果輸入的數組中有相同的字符串鍵名，則這些值會被合併到一個數組中去。如下例：

 

<?php
$arr1 = array("a"=>"PHP","C");
$arr2 = array("a"=>"JAVA","C","PYTHON");
print_r(array_merge_recursive($arr1, $arr2)); //Array ( [a] => Array ( [0] => PHP [1] => JAVA ) [0] => C [1] => C [2] => PYTHON )
?>