How to remove duplicate values ​​from php two-dimensional array

In PHP, deduplication of two-dimensional arrays is a common problem. When we need to perform data processing on an array containing multiple dimensions, we may encounter the need to integrate the values ​​of a certain dimension. At this time, if there are duplicate values, they need to be deduplicated to avoid problems caused by data duplication. This article will introduce how to deduplicate two-dimensional arrays in PHP.

Method 1: Use array_unique function

The array_unique function can be used to remove duplicate values ​​in an array and return a new array. Its use is very simple, just pass the deduplicated array to this function.

For example, for such a two-dimensional array:

$arr = array(
    array('name' => 'John', 'age' => 20),
    array('name' => 'Mary', 'age' => 25),
    array('name' => 'John', 'age' => 20),
    array('name' => 'Peter', 'age' => 22),
    array('name' => 'Mary', 'age' => 25)
);

We use the array_unique function to remove duplicates:

$result = array_unique($arr, SORT_REGULAR);
print_r($result);

The output result is:

Array
(
    [0] => Array
        (
            [name] => John
            [age] => 20
        )

    [1] => Array
        (
            [name] => Mary
            [age] => 25
        )

    [3] => Array
        (
            [name] => Peter
            [age] => 22
        )

)

You can see , the duplicate elements have been removed.

It should be noted that array_unique deduplicates all dimensions of the array by default. If we only want to deduplicate one dimension, we need to perform some special processing.

For example, if we only want to remove duplication through the name dimension, we can use the following method:

//遍历二维数组，将name作为键名
foreach($arr as $value){
    $temp_arr[$value['name']] = $value;
}
//去重后，将数组重新按照数字索引重新排序
$temp_arr = array_values($temp_arr);
print_r($temp_arr);

The output result is:

Array
(
    [0] => Array
        (
            [name] => John
            [age] => 20
        )

    [1] => Array
        (
            [name] => Mary
            [age] => 25
        )

    [2] => Array
        (
            [name] => Peter
            [age] => 22
        )

)

As you can see, we pass Using name as the key name achieves the effect of deduplicating only the name dimension.

Method 2: Use the array_reduce function

Another commonly used deduplication method is through the array_reduce function. The array_reduce function can perform a reduction operation on all elements in the array and finally return a scalar value. We can use this function to deduplicate two-dimensional arrays.

For example, for such a two-dimensional array:

$arr = array(
    array('name' => 'John', 'age' => 20),
    array('name' => 'Mary', 'age' => 25),
    array('name' => 'John', 'age' => 20),
    array('name' => 'Peter', 'age' => 22),
    array('name' => 'Mary', 'age' => 25)
);

We use the array_reduce function to remove duplicates:

//定义一个回调函数，用于去重
function filter_duplicate($carry, $item){
    if(!in_array($item, $carry)){
        $carry[] = $item;
    }
    return $carry;
}

$result = array_reduce($arr, 'filter_duplicate', array());
print_r($result);

The output result is:

Array
(
    [0] => Array
        (
            [name] => John
            [age] => 20
        )

    [1] => Array
        (
            [name] => Mary
            [age] => 25
        )

    [3] => Array
        (
            [name] => Peter
            [age] => 22
        )

)

You can see , the duplicate elements have been removed.

It should be noted that the array_reduce function will also deduplicate all dimensions of the array. If we only want to deduplicate one of the dimensions, we need to perform some special processing, similar to using the array_unique function.

Method 3: Use loop traversal

Another common deduplication method is to use loop traversal. This method is more complicated, but it can make full use of PHP's array-related functions to achieve flexible deduplication processing. We can exclude duplicate elements by using the in_array function in a loop or by hashing each element.

For example, for such a two-dimensional array:

$arr = array(
    array('name' => 'John', 'age' => 20),
    array('name' => 'Mary', 'age' => 25),
    array('name' => 'John', 'age' => 20),
    array('name' => 'Peter', 'age' => 22),
    array('name' => 'Mary', 'age' => 25)
);

We can use the following code to remove duplicates:

$new_arr = array();
foreach($arr as $value){
    $hash = md5(serialize($value)); //计算一个哈希值
    if(!isset($new_arr[$hash])){
        $new_arr[$hash] = $value; //新元素加入新数组
    }
}
$new_arr = array_values($new_arr); //将新数组重新按照数字索引重新排序
print_r($new_arr);

The output result is:

Array
(
    [0] => Array
        (
            [name] => John
            [age] => 20
        )

    [1] => Array
        (
            [name] => Mary
            [age] => 25
        )

    [2] => Array
        (
            [name] => Peter
            [age] => 22
        )

)

Yes As you can see, the duplicate elements have been removed and the new array is reordered according to the numerical index.

Summary:

The above are three common deduplication methods. Each method has its advantages and disadvantages. You need to choose the appropriate method according to the actual situation. When processing two-dimensional arrays, we should follow the principle of "simple and efficient" and use the array-related functions provided by PHP as much as possible to reduce code complexity and operating efficiency, and improve program performance.

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