Detailed usage of array_merge function in php (with examples)

This article brings you the detailed usage of the array_merge function in PHP (with examples). It has certain reference value. Friends in need can refer to it. I hope it will be helpful to you.

array_merge This function is very practical and commonly used, but it has some features that can cause trouble if you don't pay attention. This problem occurred when I was modifying my colleague's code a few days ago, so I looked up some information and wrote it down.

Definition and syntax

array array_merge (array $array1 [, array $...])
Merge one or more arrays.
If the input array has the same string key name, the value after the key name will overwrite the previous value. However, if the array contains numeric keys, the subsequent values ​​will not overwrite the original values ​​but will be appended to them.

The syntax is simple, and the return value is the merged array (not always the return value you expect).

Example

<?php // 索引数组
$arr1 = array(0 => 'apple', 1 => 'banana');
$arr2 = array(1 => 'pear', 2 => 'orange');
$arr3 = array('pitaya' => '火龙果');
print_r(array_merge($arr1, $arr2));//  array_merge会重建索引 Array ( [0] => apple [1] => banana [2] => pear [3] => orange )
echo '<br>';
print_r(array_merge($arr1, $arr2, $arr3));// 索引数组和关联数组合并 Array ( [0] => apple [1] => banana [2] => pear [3] => orange [pitaya] => 火龙果 )
echo '<br>';
// 索引数组不会覆盖，但是使用 + 的话，前面的值会覆盖后面相同索引的值
print_r($arr1 + $arr2);// Array ( [0] => apple [1] => banana [2] => orange )
echo '<br>';

// 关联数组
$arr1 = array('apple' => '苹果', 'banana' => '香蕉');
$arr2 = array('apple' => '黄元帅苹果', 'orange' => '橙子');
print_r(array_merge($arr1, $arr2));//  Array ( [apple] => 黄元帅苹果 [banana] => 香蕉 [orange] => 橙子 )
echo '<br>';
// 后面的值会覆盖前面相同key的值，而使用 + 则正好相反，前面的值会覆盖后面的值
print_r($arr1 + $arr2);// Array ( [apple] => 苹果 [banana] => 香蕉 [orange] => 橙子 )

Filling the pit

So what is the so-called pitfall of array_merge?
In actual use, the framework is used to query data from the database, and what is returned is a two-dimensional array or one-dimensional array. But if the data cannot be queried, null will be returned. If array_merge is used at this time, an error will occur. The following

<?php $arr1 = array(&#39;apple&#39;, &#39;pear&#39;);
$arr2 = null;

$arr3 = array_merge($arr1, $arr2);
var_dump($arr3);
// Warning: array_merge(): Argument #2 is not an array in D:\WWW\test.php on line 6
// NULL

will generate a Warning, and the return value of array_merge will be null.
The processing method is not difficult, just convert the parameters into an array, and you can encapsulate the function for processing. What should be noted is how to handle the parameter false. As follows

<?php /**
 * 完善 array_merge
 * 将所有参数转换为数组，null、false 转换为空数组
 * @param array ...$args
 * @return array
 */
function array_merge_perfect(...$args)
{
    $fun = function ($value) {
        if ($value === false) {
            return array();
        }

        return (array)$value;
    };

    // 将所有参数都转换为 array 类型
    $arr = array_map($fun, $args);

    $newArray = array();
    foreach ($arr as $key => $value) {
        $newArray = array_merge($newArray, $value);
    }

    return $newArray;
}

$arr1 = array('test' => array('apple', 'pear'), 'test1' => array('apple', 'pear'));
$arr2 = false;
$arr3 = null;

print_r((array)$arr2);// Array ( [0] => )
echo '<br>';
print_r((array)$arr3);// Array ( )
echo '<br>';

print_r(array_merge_perfect($arr1, $arr2));// Array ( [test] => Array ( [0] => apple [1] => pear ) [test1] => Array ( [0] => apple [1] => pear ) )
echo '<br>';
print_r(array_merge_perfect($arr1, $arr3));// Array ( [test] => Array ( [0] => apple [1] => pear ) [test1] => Array ( [0] => apple [1] => pear ) )
echo '<br>';
print_r(array_merge_perfect($arr2, $arr3));// Array ( )
echo '<br>';

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