Introduction to the usage of PHP array_flip() function

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.

1. 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.

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