php array loop conversion

In PHP programming, arrays are one of the most common data structures. Arrays allow us to store, organize, and access large amounts of related data. In many cases, we need to perform a series of operations on arrays, such as searching, sorting, filtering, etc. Among them, array loop conversion is a relatively important operation. This article will introduce in detail how to use PHP to implement array loop conversion.

1. Basic structure of array loop

In PHP, we can use for, foreach and other loop statements to loop through an array. The following is the basic structure of a for loop:

for ($i = 0; $i < count($array); $i++) {
  // do something with $array[$i]
}

The same effect can be achieved using the foreach statement:

foreach ($array as $value) {
  // do something with $value
}

2. Array conversion method

In PHP, we Arrays can be converted in the following two ways:

1. Using array functions

PHP provides a large number of functions to perform various operations on arrays, some of which Can be used to convert arrays. The following are some commonly used functions:

• array_map(): applies a callback function to each element in the array and returns a new array
• array_filter(): uses the callback function Filter the elements in the array and return a new array
• array_reduce(): Reduce the array to a single value and return that value

The following is the use of the array_map() function Example of squaring each element in an array:

$array = array(1, 2, 3, 4, 5);
$new_array = array_map(function($x){ return $x * $x; }, $array);
print_r($new_array);

The output is:

Array
(
    [0] => 1
    [1] => 4
    [2] => 9
    [3] => 16
    [4] => 25
)

Note that when using the array_map() function, we need to pass a callback function as a parameter. This callback function takes one argument (the value of each element) and returns a value to replace the element.

2. Using the loop structure

We can loop through the array and convert it through the for or foreach statement. The following is an example of using a for loop to square elements in an array:

$array = array(1, 2, 3, 4, 5);
$new_array = array();
for ($i = 0; $i < count($array); $i++) {
  $new_array[] = $array[$i] * $array[$i];
}
print_r($new_array);

The output result is also:

Array
(
    [0] => 1
    [1] => 4
    [2] => 9
    [3] => 16
    [4] => 25
)

3. Batch conversion operation

Assume we have a two dimensional array, whose data is as follows:

$data = array(
  array('name' => '张三', 'age' => 19, 'gender' => '男'),
  array('name' => '李四', 'age' => 21, 'gender' => '女'),
  array('name' => '王五', 'age' => 20, 'gender' => '男'),
);

Now we need to convert it to the following format:

$new_data = array(
  array('姓名' => '张三', '年龄' => 19, '性别' => '男'),
  array('姓名' => '李四', '年龄' => 21, '性别' => '女'),
  array('姓名' => '王五', '年龄' => 20, '性别' => '男'),
);

We can use a foreach loop to achieve this operation:

$new_data = array();
foreach ($data as $values) {
  $new_data[] = array('姓名' => $values['name'], '年龄' => $values['age'], '性别' => $values['gender']);
}
print_r($new_data);

Output results As follows:

Array
(
    [0] => Array
        (
            [姓名] => 张三
            [年龄] => 19
            [性别] => 男
        )

    [1] => Array
        (
            [姓名] => 李四
            [年龄] => 21
            [性别] => 女
        )

    [2] => Array
        (
            [姓名] => 王五
            [年龄] => 20
            [性别] => 男
        )

)

4. Notes

1. The original array will not be changed

In PHP, the loop conversion operation usually generates a new array without changing the original array. Therefore, care should be taken not to change the value of the original array when operating.

2. Callback function

When using array functions for conversion, we need to pass a callback function as a parameter. If the callback function needs to access some external variables, you need to use a closure to define the callback function to ensure that it can correctly access the external variables.

3. Index of array

In the loop conversion operation, we need to pay attention to the index of the array. If we do not explicitly specify the index of the new array, PHP will automatically assign the index value, usually starting from 0 and increasing.

5. Summary

The array in PHP is a very useful data structure, and loop conversion is a very important operation among them. We can use for, foreach loop structures, or array functions such as array_map, array_filter, array_reduce, etc. to achieve array conversion. During the operation, you need to be careful not to change the value of the original array, and you need to pay attention to the index of the array. I hope this article can help readers master array loop conversion in PHP.

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