php array to collection

In PHP, arrays and sets are very common data structures. An array is an ordered collection that can contain different types of data, such as numbers, strings, and objects. A set is more abstract and represents a collection of elements, where each element is unique and has no specific order or index.

In actual development, we often need to convert an array into a set to facilitate more efficient searches and operations. In PHP, it is very simple to implement this conversion, and this article will introduce the implementation methods and techniques.

1. Use the array_unique function

In PHP, there is a built-in function array_unique, which can be used to remove duplicate elements in an array. The basic syntax of this function is as follows:

array array_unique ( array $array [, int $sort_flags = SORT_STRING ] )

Among them, $array represents the array that needs to be deduplicated, $sort_flags represents the optional sorting method, the common ones are SORT_STRING (sorted by string), SORT_NUMERIC (sorted by numbers) Sort by way) and SORT_REGULAR (sort in natural order), etc.

If you pass an array to the array_unique function, it will return a new array containing unique elements. For example:

$arr = array(1,2,2,3,3,3);
$set = array_unique($arr);
print_r($set); // 输出 Array ( [0] => 1 [1] => 2 [3] => 3 )

It can be seen that using the array_unique function can easily convert an array into a set.

2. Use the array_flip function

In addition to using the array_unique function, there is another simple way to convert an array into a collection, which is to use the array_flip function. This function is used to exchange the keys and values ​​in the array, that is, the values ​​in the array are used as the keys of the new array, and the original keys are ignored. The basic syntax of the function is as follows:

array array_flip ( array $array )

Among them, $array represents the array whose keys and values ​​need to be exchanged. If you pass an array to the array_flip function, it will return a new array with the values ​​in the original array as keys and all values ​​in the new array. For example:

$arr = array('a', 'b', 'c');
$set = array_flip($arr);
print_r($set); // 输出 Array ( [a] => 0 [b] => 1 [c] => 2 )

Since the elements in the collection must be unique, we can ignore the values ​​in the new array and only keep its keys, that is:

$arr = array('a', 'b', 'c');
$set = array_flip($arr);
$set = array_keys($set);
print_r($set); // 输出 Array ( [0] => a [1] => b [2] => c )

In this way, we get a A collection containing all elements in the original array.

3. Use the array_reduce function

Another commonly used method is to use the array_reduce function. This function is used to iteratively calculate all elements in the array and return a final result. The basic syntax of the function is as follows:

mixed array_reduce ( array $array , callable $callback [, mixed $initial = NULL ] )

Among them, $array represents the array that needs to be iteratively calculated, $callback is a callback function used to calculate the elements in the array, $initial is an optional initial value, Used to specify the initial state during the iteration process. The basic syntax of the callback function is as follows:

mixed function callback ( mixed $carry , mixed $item )

Among them, $carry represents the result of the previous iteration, and $item represents the element of the current iteration. The callback function generates a new calculation result based on the last calculation result and the current element, and returns it to the array_reduce function for the next iteration.

In order to convert an array into a collection, we need to use the technique of deduplication in the callback function. Specifically, we can use the array reference technique in PHP to use the value as the key in the collection and set the value itself to 1 to ensure that the value corresponding to each key is 1, thereby ensuring that the elements in the collection are unique. The code is as follows:

$arr = array(1,2,2,3,3,3);
$set = array_reduce($arr, function(&$res, $cur){
    $res[$cur] = 1;
    return $res;
}, array());
print_r(array_keys($set)); // 输出 Array ( [0] => 1 [1] => 2 [2] => 3 )

Through the processing of the above callback function, we successfully converted the original array into a collection. Of course, we can also use other set-specific operations in the callback function, such as intersection, union, difference, etc.

Summary

Converting an array to a collection is very common in actual development. PHP provides several ways to accomplish this conversion, including using the built-in functions array_unique, array_flip, and array_reduce, each with their own pros and cons. In actual scenarios, developers can choose different methods according to specific situations to ensure code efficiency and readability.

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