How to get array key-value pairs in php

With the increasing popularity of web development, PHP language has become one of the most commonly used server-side scripting languages. In PHP, array is a very common data type that allows us to store multiple variables in the same variable. But what should we do when we need to get the key-value pairs in the array? This article will introduce how to obtain array key-value pairs in PHP.

1. Use foreach to traverse the array

The simplest method may be to use a foreach loop to traverse the array and then obtain each key-value pair. The sample code is as follows:

$array = array('foo' => 'bar', 'baz' => 'qux');

foreach ($array as $key => $value) {
    echo "Key: $key; Value: $value\n";
}

The above code will output the following results:

Key: foo; Value: bar
Key: baz; Value: qux

In this example, we store an associative array containing two key-value pairs in the variable $array. Then, we use a foreach loop to iterate through the array and obtain each key-value pair through the $key and $value variables. On each iteration, output the key and value of a key-value pair.

2. Use the array_keys and array_values ​​functions

In addition to using the foreach loop to traverse the array, you can also use the PHP built-in functions array_keys and array_values ​​to obtain the keys and values ​​of the array respectively. The sample code is as follows:

$array = array('foo' => 'bar', 'baz' => 'qux');

$keys = array_keys($array);
$values = array_values($array);

print_r($keys);
print_r($values);

The above code will output the following results:

Array
(
    [0] => foo
    [1] => baz
)
Array
(
    [0] => bar
    [1] => qux
)

In this example, we first define an associative array $array containing two key-value pairs. We then use the array_keys function to get the keys of the array and store them in the variable $keys. Likewise, we use the array_values ​​function to get the values ​​of the array and store them in the variable $values. Finally, use the print_r function to output the contents of the $keys and $values ​​arrays respectively.

3. Use the array_map function

Another way to obtain array key-value pairs is to use the array_map function. This function will accept a callback function and one or more arrays as parameters and apply the callback function to the corresponding element in each array. The following is a sample code that uses the array_map function to obtain the array key-value pairs:

$array = array('foo' => 'bar', 'baz' => 'qux');

$keyValuePairs = array_map(function($key, $value){
    return array('key' => $key, 'value' => $value);
}, array_keys($array), array_values($array));

print_r($keyValuePairs);

The above code will output the following results:

Array
(
    [0] => Array
        (
            [key] => foo
            [value] => bar
        )

    [1] => Array
        (
            [key] => baz
            [value] => qux
        )

)

In this example, we use the array_keys and array_values ​​functions to obtain the array's key-value pairs. keys and values, and pass them respectively as arguments to the array_map function. Then, we define a callback function that accepts two parameters $key and $value and returns an associative array containing the 'key' and 'value' keys. Finally, we use the print_r function to output the contents of the $keyValuePairs array.

4. Use the array_walk function

Similar to the array_map function, the array_walk function can also be used to obtain the key-value pairs of the array. This function will accept a callback function and an array as parameters and apply the callback function to each element in the array. The following is an example code that uses the array_walk function to obtain array key-value pairs:

$array = array('foo' => 'bar', 'baz' => 'qux');

$keyValuePairs = array();
array_walk($array, function($value, $key) use (&$keyValuePairs){
    $keyValuePairs[] = array('key' => $key, 'value' => $value);
});

print_r($keyValuePairs);

The above code will output the following results:

Array
(
    [0] => Array
        (
            [key] => foo
            [value] => bar
        )

    [1] => Array
        (
            [key] => baz
            [value] => qux
        )

)

In this example, we define an empty array $keyValuePairs, And use the array_walk function to walk through the array. The callback function accepts two parameters $value and $key, and uses the use keyword to reference the external variable $keyValuePairs. On each iteration, add an associative array containing the 'key' and 'value' keys to the $keyValuePairs array. Finally, use the print_r function to output the contents of the $keyValuePairs array.

Summary

This article introduces four methods of obtaining array key-value pairs in PHP. Using a foreach loop to iterate over an array is the simplest and common way. If you only need to get the keys or values ​​of an array, you can use the array_keys or array_values ​​functions. The array_map and array_walk functions can be used to obtain an array containing key-value pairs, but they require more code to implement. No matter which method you choose, these tips are very useful and can help you manipulate arrays more easily.

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