How to modify a value in an array in php

In PHP development, operating arrays is one of the operations that is often encountered. When operating an array, sometimes you need to modify a value in the array. So in PHP, how to modify a value in an array? The following will introduce it to you in detail.

1. Use a for loop to traverse the array to modify the value

The most basic method is to use a for loop to traverse the array and modify the value that needs to be modified. The specific implementation is as follows:

<?php $arr = [1, 2, 3, 4, 5];
for($i = 0; $i < count($arr); $i++) {
    if($arr[$i] == 2) {
        $arr[$i] = 20;
    }
}
print_r($arr);
?>

In the above code, we define an array $arr containing 5 elements, then traverse the array through a for loop, and use the if statement to determine whether the element is equal to 2. If it equals 2, modify it to 20. Finally, we call the print_r() function to output the modified array.

It is worth noting that this method is suitable for only one value in the array that needs to be modified. If there are multiple values ​​that need to be modified, the array needs to be traversed multiple times, and the efficiency will become relatively low.

2. Use foreach loop to modify array values

In addition to for loop, we can also use foreach loop to traverse the array and modify the value. The specific implementation is as follows:

<?php $arr = [
    [&#39;name&#39; => 'Tom', 'age' => 18],
    ['name' => 'Lucy', 'age' => 20],
    ['name' => 'John', 'age' => 22],
];

foreach($arr as &$val) {
    if($val['name'] == 'Lucy') {
        $val['age'] = 21;
    }
}

print_r($arr);
?>

In the above code, we define a two-dimensional array $arr containing 3 elements, where each sub-array contains two key-value pairs: name and age. We can use a foreach loop to traverse the array and use an if statement to determine whether name is equal to Lucy. If it is equal to Lucy, modify its age to 21. It should be noted here that we use the & symbol before the loop variable $val, indicating that $val is a reference, and modifying its value will directly modify the value in the original array.

3. Use the array_map() function to modify the array value

PHP provides a very convenient function array_map(), which can execute a callback function for each element in the array. Through this function, we can easily modify a value in the array.

<?php $arr = [1, 2, 3, 4, 5];
$arr = array_map(function($val) {
    if($val == 2) {
        return 20;
    }
    return $val;
}, $arr);
print_r($arr);
?>

In the above code, we call the array_map() function and pass in the anonymous function as the first parameter. The function of this anonymous function is to determine whether the element is equal to 2. If it is equal to 2, return 20, otherwise return the element itself. Finally, we output the modified array.

4. Use the array_walk() function to modify the array value

Similar to the array_map() function, PHP also provides another function array_walk() for applying to each element in the array User-defined functions. Specific examples are as follows:

<?php $arr = [
    [&#39;name&#39; => 'Tom', 'age' => 18],
    ['name' => 'Lucy', 'age' => 20],
    ['name' => 'John', 'age' => 22],
];

function changeAge(&$val, $key) {
    if($val['name'] == 'Lucy') {
        $val['age'] = 21;
    }
}

array_walk($arr, 'changeAge');
print_r($arr);
?>

In the code, we define a function changeAge() to determine whether the name of the subarray in the array is equal to Lucy. If it is equal to Lucy, modify its age to 21. Then, we call the array_walk() function, passing changeAge() as the second parameter. It should be noted here that the first parameter $val of the changeAge() function is a reference type, that is, modifying the value of $val will directly modify the value in the original array.

Summary:

Through the above four methods, we can easily modify a value in the array. The most appropriate method needs to be considered based on the actual situation. Of course, in addition to the above methods, there are other methods to modify the values ​​in the array, such as using the array_replace() function, reference cycles, etc. Don't forget that when modifying the values ​​in the array, you must pay attention to the correctness of the logic to avoid unnecessary consequences.

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