PHP language is a widely used Web programming language. Arrays are a very commonly used data structure during the development of Web applications. The key-value pairs in the array allow programmers to organize and manage data conveniently. PHP's array_flip() function is a very useful function. It can exchange the keys and values of the array, using the original keys as values and the original values as keys. This article will introduce you to the usage of PHP's array_flip() function and its application in actual programming.
- Basic usage of array_flip() function
The array_flip() function in PHP can exchange the keys and values of an array, that is, the original keys become Values, which were originally values, become keys. Its syntax format is as follows:
array array_flip ( array $array )
Parameter description:
- array: Array that needs to be exchanged for key/value pairs
Return value: Return A new array in which the keys of the original array become the values of the new array and the values of the original array become the keys of the new array.
The following is an example of using the array_flip() function:
$old_array = array("apple"=>"fruit", "carrot"=>"vegetable"); $new_array = array_flip($old_array); var_dump($new_array);
In this example, the old array $old_array contains 2 elements, namely "apple" and "carrot". Their values are "fruit" and "vegetable" respectively. This array uses the form of an associative array. After calling the array_flip() function, it will return a new array $new_array. In $new_array, "fruit" and "vegetable" become the keys of the new array, and "apple" and "carrot" become the values of the new array. Finally, we use the var_dump() function to output the new array. The output result is as follows:
array(2) { ["fruit"]=> string(5) "apple" ["vegetable"]=> string(6) "carrot" }
2. Using the array_flip() function in programming
The use of the array_flip() function is very simple, but in practice It may be used frequently in programming.
This section will introduce some example uses of the array_flip() function in programming.
2.1 Usage 1: Delete duplicate items in the array
Elements in the array may be duplicated. If you need to delete duplicate elements in an array, you can first use the array_flip() function to exchange the key-value pairs of the array, so that you can use the array_unique() function to delete the duplicate keys, and finally use the array_flip() function to restore the key/value pairs. to its original form. The specific example is as follows:
$old_array = array("apple", "banana", "carrot", "apple", "grape", "banana"); $new_array = array_flip($old_array); $new_array = array_unique($new_array); $new_array = array_flip($new_array); print_r($new_array);
Run this program, the output result is:
Array ( [0] => apple [1] => banana [2] => carrot [4] => grape )
By using the array_flip() function, we first exchange the keys and values of the array, and then use the array_unique() function Duplicate keys in the array are removed, and finally the keys and values of the array are restored using the array_flip() function.
2.2 Usage 2: Find the value in the array
Use the array_flip() function to quickly find the key corresponding to a value in the array. If a value is unique, you can first use the array_flip() function to exchange the key and value, and then use the array_key_exists() function or isset() function to determine whether the key corresponding to this value exists. The specific example is as follows:
$old_array = array("apple"=>"fruit", "banana"=>"fruit", "carrot"=>"vegetable"); $new_array = array_flip($old_array); if (isset($new_array["fruit"])) { echo "fruit is found in array"; }
The output result is:
fruit is found in array
In the above code, we exchange the keys and values of the $old_array array, and then use the isset() function to find the new array Whether the value "fruit" exists in $new_array, because the array has been exchanged, so we are actually looking for the key "fruit" in the original array $old_array. Running the program, the output is "fruit is found in array".
2.3 Usage 3: Generate enumeration array
In program development, sometimes it is necessary to define a limited number of sets, such as weeks, seasons, etc. You can use the array_flip() function to use the values in an array as the keys of a new array, and then use the range() function to generate a sequence of numbers in a specified range as the value of the new array. The specific example is as follows:
$old_array = array("Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday", "Sunday"); $new_array = array_flip($old_array); $enum_array = array_map(function(){static $index = 1; return $index++;}, range(1, count($old_array))); $new_array = array_replace($new_array, $enum_array); print_r($new_array);
The output result is:
Array ( [Monday] => 1 [Tuesday] => 2 [Wednesday] => 3 [Thursday] => 4 [Friday] => 5 [Saturday] => 6 [Sunday] => 7 )
In the above code, we first use the array_flip() function to exchange the keys and values of the original array, and then use the range() function Generate a sequence with the length of the original array, and then use the array_map() function to replace this sequence with the value of the new array. Finally, we use the array_replace() function to merge this enumeration array with the original array of key/value pairs to form a new array with enumeration values.
The above is the detailed content of Introduction to the usage of PHP array_flip() function. For more information, please follow other related articles on the PHP Chinese website!

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