How to efficiently find the difference set of two-dimensional arrays in PHP

During the PHP development process, we often need to perform some operations on arrays, such as array merging, deduplication, intersection, union, etc. Array difference is a very important type of array operation. It can help us find different parts of two arrays efficiently. In this article, we will introduce how to use PHP language to efficiently find the difference set of two-dimensional arrays.

1. What is a two-dimensional array

Before we start learning how to find the difference set of a two-dimensional array, we first need to understand what a two-dimensional array is. A two-dimensional array means that each element in an array is an array, that is, an array contains multiple arrays. Two-dimensional arrays are very common in practical applications, such as processing data tables, statistical data, etc., so we need to master how to operate two-dimensional arrays.

2. Calculate the difference between two arrays

In PHP, we can use the array_diff function to calculate the difference between two one-dimensional arrays, but for two-dimensional arrays In other words, we need to use some other methods to solve it. Next we will introduce how to calculate the difference set of two two-dimensional arrays.

Suppose we have two two-dimensional arrays $firstArray and $secondArray. We need to calculate their difference and save the difference into $resultArray. We can use the following code:

$resultArray = array();
foreach($firstArray as $firstItem){
    $flag = true;
    foreach($secondArray as $secondItem){
        if($firstItem == $secondItem){
            $flag = false;
            break;
        }
    }
    if($flag){
        $resultArray[] = $firstItem;
    }
}

In the above code, we use two foreach loops to traverse two two-dimensional arrays and store their elements in $firstItem and $secondItem respectively. Then we use the variable $flag to mark whether the conditions are met. If $firstItem already exists in $secondArray, set $flag to false. Finally, if $flag is still equal to true, it means $firstItem does not exist in $secondArray and we need to store it in $resultArray.

Although the above method is feasible, it is relatively inefficient when we deal with large-scale two-dimensional arrays. To improve performance, we can use some PHP functions to simplify the above code.

3. Using the array_udiff function

PHP provides an array_udiff function, which can be used to calculate the difference between two arrays (or multiple arrays). The function of this function is the same as the foreach loop above, but it is more efficient than the foreach loop. We can use the following code to calculate the difference between two two-dimensional arrays:

function compareArray($a, $b) {
    return $a == $b ? 0 : 1;
}
$resultArray = array_udiff($firstArray, $secondArray, 'compareArray');

In the above code, we have customized a function compareArray to determine whether two elements are equal. Returns 0 if equal, 1 otherwise. When calling the array_udiff function, we pass in two two-dimensional arrays $firstArray and $secondArray, and the custom function compareArray as parameters. The array_udiff function compares the elements in the two arrays based on the compareArray function, removes identical elements, and finally returns the difference between the two arrays.

4. Using the array_map and array_column functions

In addition to using the array_udiff function, we can also use the array_map and array_column functions to process the difference set of two-dimensional arrays. The array_map function applies a specified function to each element in the array and returns a new array. The array_column function can extract columns from a two-dimensional array and return a new one-dimensional array.

Below we combine the above two functions and use the following code to calculate the difference set of two two-dimensional arrays:

$diffArray = array_map(function($item) use($secondArray) {
    $existKey = array_search($item['id'], array_column($secondArray, 'id'));
    return $existKey === false ? $item : null;
}, $firstArray);
$resultArray = array_filter($diffArray);

In the above code, we use the array_map function to convert $firstArray into Each element of is applied to an anonymous function. In the anonymous function, we use the array_search function to find if the same element exists in $secondArray. Returns null if present, otherwise returns the element. Finally, we use the array_filter function to delete null values, and finally get the difference set of the two two-dimensional arrays.

5. Summary

Array difference is an operation often used in PHP development, which can help us efficiently find different values ​​in two two-dimensional arrays. part. In this article, we introduced three methods to calculate the difference of two-dimensional arrays: using a foreach loop, array_udiff function, array_map and array_column functions. Compared with the foreach loop, the latter two methods are more efficient and more efficient when processing large-scale two-dimensional arrays. In the actual development process, we should choose the most appropriate method based on the actual situation.

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