PHP array value query key

In PHP programming, arrays are a very important data type, especially in web development. When using an array, it is often necessary to query the corresponding key value through the value value of the array. This article will introduce some commonly used methods and techniques to help readers better implement this function.

1. array_search() function

PHP provides a built-in function array_search(), which can be used to find the key value corresponding to the specified value in the array. The basic syntax of this function is as follows:

array_search($value, $array, $strict);

Among them, $value indicates the value to be found, $array indicates the array to be found, and $strict indicates whether to perform strict comparison. If $strict=true, then data types and values ​​need to be compared; otherwise only values ​​need to be compared.

For example:

$array = ['a' => 1, 'b' => 2, 'c' => 3];
$key = array_search(2, $array);
echo $key; // 输出：b

$key = array_search('2', $array);
echo $key; // 输出：b

$key = array_search(2, $array, true);
echo $key; // 输出：b

$key = array_search('2', $array, true);
echo $key; // 输出：空

It should be noted that this function only returns the first queried key value. If there are multiple elements with the same value, only one of the key values ​​can be returned.

2. array_keys() function

Another commonly used function is array_keys(), which can be used to obtain all key values ​​in the array that satisfy the specified value. The syntax of this function is as follows:

array_keys($array, $value, $strict);

Among them, $array represents the array to be searched, $value represents the value to be searched, and $strict represents whether to perform strict comparison.

For example:

$array = ['a' => 1, 'b' => 2, 'c' => 2];
$keys = array_keys($array, 2);
print_r($keys); // 输出：[b, c]

$keys = array_keys($array, '2', true);
print_r($keys); // 输出：空

$keys = array_keys($array, 2, true);
print_r($keys); // 输出：[b]

It should be noted that this function returns an array that contains all key values ​​that meet the conditions. If no matching key value is found, an empty array is returned.

3. foreach loop

In addition to using built-in functions, we can also query the key value corresponding to a certain value by traversing the entire array. Here we can use PHP’s foreach loop statement to achieve this. The specific method is to use the if conditional statement during the loop to determine whether the value of the current element is equal to the specified value. If equal, the key value of the current element is returned.

For example:

$array = ['a' => 1, 'b' => 2, 'c' => 3];
$value = 2;

foreach ($array as $key => $val) {
    if ($val == $value) {
        echo 'key: ' . $key . '<br/>';
    }
}

// 输出：key: b

It should be noted that using foreach loop to traverse the entire array is less efficient. Therefore, it is recommended to use built-in functions like array_search() and array_keys() when dealing with large amounts of data.

4. array_flip() function

Sometimes, we want to interchange the key and value of the array. In this case, we can use the array_flip() function. This function can quickly interchange keys and values ​​in an array. For example:

$array = ['a' => 1, 'b' => 2, 'c' => 3];
$new_array = array_flip($array);
print_r($new_array);

The output result is:

Array
(
    [1] => a
    [2] => b
    [3] => c
)

At this time, we only need to query the key value corresponding to the value value in the new array. It should be noted that if there are multiple identical value values, only one of the key values ​​can be returned.

Summary

Arrays are a very important data type in PHP programming. Programmers usually need to know how to obtain the corresponding key value through the value value in the array. This article describes four implementation methods, including the array_search() function, array_keys() function, foreach loop, and array_flip() function. Programmers can choose the appropriate method based on specific needs. At the same time, you need to pay attention to some details, such as whether to perform strict comparison, whether to return an array or a single value, etc. Through in-depth understanding and practice, we can better master this common operation, thereby improving the efficiency and robustness of our code.

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