How to change the value of a two-dimensional array in PHP

In PHP, two-dimensional array is a very common data type. When processing data, we often need to modify the values ​​​​of two-dimensional arrays. In this article, we will discuss how to change the value of a two-dimensional array in PHP.

First, we need to understand the structure of a two-dimensional array and how to access its values.

A two-dimensional array usually consists of multiple arrays, each array contains multiple key-value pairs. For example, the following is a simple two-dimensional array:

$students = array(
    array("name" => "Tom", "age" => 18),
    array("name" => "Jerry", "age" => 20),
    array("name" => "Alice", "age" => 19)
);

This two-dimensional array contains three arrays, each array has two key-value pairs: name and age .

To access the values ​​in a two-dimensional array, we need to use two square brackets. The first square bracket contains an integer, which is used to access the subarray in the array; the second square bracket contains a string, which is used to access the key-value pair in the subarray. For example, to access the name value of the first subarray in $students, we can use the following code:

echo $students[0]["name"]; // 输出 Tom

Now, we will discuss how to change the 2D the values ​​in the array. The most common way is to use the square bracket syntax above for assignment. For example, to change the age value of the first subarray in $students from 18 to 20, you would use the following code:

$students[0]["age"] = 20;

This will change the first The age value of the subarray changes from 18 to 20.

We can also use a loop to traverse the entire two-dimensional array and modify each value in it. Here is a sample code that will increase the age of all students by 2 years:

foreach ($students as &$student) {
    $student["age"] += 2;
}

This will loop through each student, increase their age by 2 years, and update that value in their original array.

It should be noted that if we do not use the & symbol, the values ​​in the final array will not be modified. Because in a loop, PHP passes a copy of the value by default, not a reference to the value. Using the & notation ensures that we directly modify the values ​​in the original array.

There is another situation where we may need to add a new subarray to the two-dimensional array and set its key-value pairs. In order to do this, we can use PHP's array_push() function, which adds a new subarray to an existing two-dimensional array. For example, the following code will add a new student named Bob:

$newStudent = array("name" => "Bob", "age" => 21);
array_push($students, $newStudent);

In the above code, $newStudent is a new associative array that represents Information about Bob's students. We then add it to the existing $students array using the array_push() function.

To sum up, it is not difficult to change the value of a two-dimensional array in PHP. We can use square bracket syntax to directly modify the key-value pairs of a single array, use a loop to traverse the entire array and modify multiple values, or use the array_push() function to add a new array. The powerful PHP language provides many methods to process data, and two-dimensional arrays are one of the indispensable data types in our development.

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