How to get the keys of an array in php

PHP is a widely used scripting language. It is characterized by being easy to learn and write, and this language has also been widely used, especially in Web development. In PHP, arrays are an important data type and are often used in web development. Obtaining the keys of an array is one of the more common operations, so this article will introduce the relevant methods of obtaining array keys in PHP.

1. Use the array_keys() function

The array_keys() function is used to return all key names in the array in the form of a new array. The following is an example:

$colors = array("red", "green", "blue");
$keys = array_keys($colors);
print_r($keys);

The above code will return:

Array
(
    [0] => 0
    [1] => 1
    [2] => 2
)

As you can see, the returned array contains all the key names of the original array, and the index of the key name is also from 0 starts.

2. Use foreach loop

The foreach statement is a common method of traversing an array. It can loop through the keys and values ​​in the array, and can use the form $key => $value to get the keys and values ​​of the array. The following code demonstrates how to use a foreach loop to traverse an array and obtain the keys:

$colors = array("red", "green", "blue");
foreach($colors as $key => $val){
  echo "键：" . $key . ", 值：" . $val . "<br/>";
}

The above code will return:

键: 0, 值: red
键: 1, 值: green
键: 2, 值: blue

As you can see, the key name of the array is stored in the $key variable.

3. Use array_keys() function combined with array_combine() function

When the key name of the array is generated by another array or a number in the range, using array_keys() may not meet expectations. the result of. At this time, you can use the array_combine() function to combine the key names and key values ​​into a new array, and then use array_keys() to return the key names of the new array. The following is an example:

$numbers = array(1, 2, 3, 4, 5);
$newArray = array_combine(range(1, count($numbers)), $numbers);
$keys = array_keys($newArray);
print_r($keys);

The above code will return:

Array
(
    [0] => 1
    [1] => 2
    [2] => 3
    [3] => 4
    [4] => 5
)

As you can see, the $keys array contains all the key names of $newArray.

Summary:

This article introduces three common methods to get the keys of PHP arrays. Using the array_keys() function is the most common method, but it may not fit all situations. Using a foreach loop can output the key-value pairs in the array, but additional processing of the key name variables is required. Combining the usage of array_combine() and array_keys() can obtain the key name of the array in a more flexible way. No matter which method is used, you need to choose the appropriate method according to the actual situation in order to better use PHP arrays.

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