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In PHP, the array_diff_key() function is used to compare the differences in key names (keys) between two arrays. Its purpose is to return elements in the first array that are different from the key value (key) of the second array. If a key exists in the second array, the elements corresponding to the key are excluded.
The main application scenario of this function is that when dealing with multiple associative arrays, you need to find out which keys exist in one array but are missing in another. Especially when performing data filtering or merging, array_diff_key() is a very useful tool.
array_diff_key(array $array1, array $array2, array ...$arrays): array
Parameter description:
$array1 : The first array, used for comparison.
$array2 : The second array for comparison.
$arrays : You can choose to pass in multiple arrays for comparison.
Return value:
Returns a new array containing all key-value pairs that exist in $array1 but are missing in $array2 .
Suppose we have two arrays $array1 and $array2 and want to find out which keys exist in $array1 but not in $array2 :
<?php
$array1 = [
"a" => 1,
"b" => 2,
"c" => 3,
"d" => 4
];
$array2 = [
"b" => 2,
"c" => 3
];
$result = array_diff_key($array1, $array2);
print_r($result);
?>
Output:
Array
(
[a] => 1
[d] => 4
)
In this example, the array_diff_key() function returns the keys a and d in $array1 because they do not appear in $array2 .
If you want to compare multiple arrays at the same time, you can pass multiple arrays as parameters:
<?php
$array1 = [
"a" => 1,
"b" => 2,
"c" => 3,
"d" => 4
];
$array2 = [
"b" => 2,
"c" => 3
];
$array3 = [
"a" => 1,
"d" => 4
];
$result = array_diff_key($array1, $array2, $array3);
print_r($result);
?>
Output:
Array
(
[a] => 1
)
In this example, array_diff_key() compares three arrays and eventually returns only a key-value pairs, as it does not exist in the other two arrays.
array_diff_key() is commonly used in the following scenarios:
Data filtering : For example, when processing user data, if you want to find which fields do not exist in a preset configuration, you can use this function to filter.
Comparison configuration files : This function can compare different versions of configuration arrays to find out which configuration item has been removed or modified.
Handle key differences in multi-dimensional arrays : If your array is a multi-dimensional array, you can combine functions such as array_map() to perform more complex operations to find different key-value pairs.
array_diff_key() compares the key names of the array, not the key values. If you need to compare the value differences in an array, you can use array_diff() .
This function preserves the key names and key values in $array1 . If you want to keep the values of the array instead of the key-value pair, consider using other methods (such as array_values() ) to get the final result.
array_diff_key() is a very useful function, especially suitable for comparing key differences in arrays. Through this function, we can easily find out which keys in an array are not available in other arrays, thereby helping us filter and process data. In actual development, it is widely used in data verification, configuration file comparison and differentiated operations of arrays.
