Tác dụng của hàm array_reduce()
The array_reduce() function iteratively reduce the array to a single value using a callback function.
It basically applies a callback function to each element of the array to build a single value.
The following table summarizes the technical details of this function.
| Return Value: | Returns the resulting value. |
|---|---|
| Changelog: | Since PHP 5.3.0, the initial parameter accepts multiple types or mixed (but not necessarily all). Previously, only integers are allowed. |
| Version: | PHP 4.0.5+ |
Syntax
The basic syntax of the array_reduce() function is given with:
The following example shows the array_reduce() function in action.
Example
Run this code »<?php
// Defining a callback function
function sum($carry, $item){
$carry += $item;
return $carry;
}
// Sample array
$numbers = array(1, 2, 3, 4, 5);
var_dump(array_reduce($numbers, "sum")); // int(15)
?>Note: The callback function has two arguments carry and item: the first one holds the value returned by the previous iteration, and the second one is the current array element.
Parameters
The array_reduce() function accepts the following parameters.
| Parameter | Description |
|---|---|
| array | Required. Specifies the array to work on. |
| callback | Required. Specifies the name of the callback function. |
| initial | Optional. Specifies the value to be used at the beginning of the process. |
More Examples
Here're some more examples showing how array_reduce() function actually works:
The following example will calculate the multiplication of array values. Since we've also specified an initial value, so the resulting value will be 1200 (because of: 10*1*2*3*4*5).
Example
Run this code »<?php
// Defining a callback function
function multiply($carry, $item){
$carry *= $item;
return $carry;
}
// Sample array
$numbers = array(1, 2, 3, 4, 5);
var_dump(array_reduce($numbers, "multiply", 10)); // int(1200)
?>If the array is empty the initial value will be used as a final result, as shown here.
Example
Run this code »<?php
// Defining a callback function
function sum($carry, $item){
$carry += $item;
return $carry;
}
// Sample array
$empty = array();
var_dump(array_reduce($empty, "sum", "No data to reduce")); // string(17)
?>If the array is empty and initial is not passed, the array_reduce() function returns NULL.