How to return an array of specified key-value pairs in php

In PHP, an array is a data structure composed of one or more key-value pairs. When we need to return the key-value pairs specified in the array, we can use some functions and methods provided in PHP. Next, let's introduce some methods that can be used to return specified key-value pairs in an array.

1. array_column() function

array_column() function can extract a single column in a multi-dimensional array as a new array, we can use it to return the specified key-value pair in the array .

Function format:

array array_column(array $input, mixed $column_key, mixed $index_key = null)

Parameter description:

• $input: the multi-dimensional array from which the value needs to be extracted.
• $column_key: The column key name or index number to be extracted.
• $index_key (optional): The key name of the new array.

Example:

$arr = array(
    array('id' => 1, 'name' => 'Tom', 'age' => 20),
    array('id' => 2, 'name' => 'Jerry', 'age' => 22),
    array('id' => 3, 'name' => 'Alice', 'age' => 21),
);

$new_arr = array_column($arr, 'name', 'id');

print_r($new_arr);

Output result:

Array
(
    [1] => Tom
    [2] => Jerry
    [3] => Alice
)

In the above example, we use the array_column() function to extract each element in the original array $arr The name is used as the value of the new array, and the id of each element is used as the key name of the new array, and the result is returned.

2. array_filter() function

array_filter() function filters the elements in the array. It can filter out the elements that meet the requirements according to the specified conditions, or it can also filter out the elements that do not meet the requirements. required elements.

Function format:

array array_filter(array $input, callable $callback = null, int $flag = 0)

Parameter description:

• $input: Array to be filtered.
• $callback (optional): filtered callback function.
• $flag (optional): Type of filtering.

Example:

$arr = array(
    array('id' => 1, 'name' => 'Tom', 'age' => 20),
    array('id' => 2, 'name' => 'Jerry', 'age' => 22),
    array('id' => 3, 'name' => 'Alice', 'age' => 21),
);

$new_arr = array_filter($arr, function($item) {
    return $item['id'] == 1;
});

print_r($new_arr);

Output result:

Array
(
    [0] => Array
        (
            [id] => 1
            [name] => Tom
            [age] => 20
        )

)

In the above example, we use the array_filter() function to filter out the items with id equal to 1 in the $arr array elements and return them into a new array.

3. array_reduce() function

The array_reduce() function can iterate over each element in the array and combine them into a single value.

Function format:

mixed array_reduce(array $input, callable $function, $initial = null)

Parameter description:

• $input: Array that needs to be iterated.
• $function: The processing function for each element.
• $initial (optional): initial value.

Example:

$arr = array(
    array('id' => 1, 'name' => 'Tom', 'age' => 20),
    array('id' => 2, 'name' => 'Jerry', 'age' => 22),
    array('id' => 3, 'name' => 'Alice', 'age' => 21),
);

$new_arr = array_reduce($arr, function($result, $item) {
    $result[$item['id']] = $item['name'];
    return $result;
});

print_r($new_arr);

Output result:

Array
(
    [1] => Tom
    [2] => Jerry
    [3] => Alice
)

In the above example, we use the array_reduce() function to reduce the value of each element in the $arr array name and id form a new key-value pair, and finally return a new array.

Summary

The above are several ways for PHP to return specified key-value pairs in an array. We can choose the appropriate method based on specific needs. It should be noted that using the array_column() function only returns a single-column array, and cannot return an array containing all original key-value pairs. Using the array_filter() and array_reduce() functions can return an array containing the original key-value pairs, but it also needs to be processed according to specific needs.

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