Questions tagged [array-reduce]

An array reduce function allows you to implement a reduce algorithm by using a callback function to iteratively reduce an array to a single value.

Documentation

• PHP: array_reduce()
• JavaScript: Array.prototype.reduce()
• Scala: Array.reduce()

Example

Consider this simple code, which will result in calculating a total value of 15 by calling the sum() function 5 times.

PHP:

function sum($total, $item) {
    return $total + $item;
}

$data = array(1, 2, 3, 4, 5);

$result = array_reduce($data, 'sum', 0);

JavaScript:

const sum = (total, item) => total + item;

const data = [1, 2, 3, 4, 5];

const result = data.reduce(sum, 0);

The sum() function will be called 5 times, once for each element of the array:

• The first time, it uses the starting value of 0 that we provided, and processes the first item:

    sum(0, 1) // returns 1
  

• The second time, it uses the return value from the first call, and processes the second item:

    sum(1, 2) // returns 3
  

• Each time after that, it uses the previous return value, and processes the next item in the array:

    sum(3, 3) // return 6
    sum(6, 4) // returns 10
    sum(10, 5) // returns 15
  

• And finally, the value returned from the last call is returned back as the result of the array_reduce() function:

    $result = 15;