Array reduce function in PHP - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the array_reduce function do in PHP?

It takes an array and reduces it to a single value by applying a callback function to each element, accumulating the result.

beginner

What are the parameters of array_reduce?

1. The input array<br>2. A callback function that takes the accumulator and current item<br>3. An optional initial value for the accumulator

intermediate

How does the callback function used in array_reduce work?

It receives two arguments: the accumulator (which stores the ongoing result) and the current array element. It returns the updated accumulator.

intermediate

What happens if you don't provide an initial value to array_reduce?

The first element of the array is used as the initial accumulator value, and the reduction starts from the second element.

beginner

Give a simple example of using array_reduce to sum numbers in an array.

Example:<br>

$numbers = [1, 2, 3, 4];
$sum = array_reduce($numbers, fn($carry, $item) => $carry + $item, 0);
echo $sum; // Outputs 10

What does the accumulator represent in array_reduce?

A The ongoing result of the reduction

B The current element of the array

C The original array

D The callback function

The accumulator holds the result as it is built up by processing each element.

What is the default initial value of the accumulator if not provided in array_reduce?

A An empty array

B null

C 0

D The first element of the array

If no initial value is given, the first element of the array is used as the initial accumulator.

Which of these is a valid callback signature for array_reduce?

A function($array) { return array_sum($array); }

B function($item, $accumulator) { return $item + $accumulator; }

C function($accumulator, $item) { return $accumulator + $item; }

D function() { return 0; }

The callback must accept accumulator first, then current item, and return the updated accumulator.

What will array_reduce return if the input array is empty and no initial value is given?

A null

B 0

C false

D An error

If the array is empty and no initial value is provided, array_reduce returns null.

Which PHP function is best for combining all elements of an array into a single value?

A array_filter

B array_reduce

C array_map

D array_merge

array_reduce is designed to reduce an array to a single value using a callback.

Explain how array_reduce works in PHP and describe its parameters.

Think about how you would combine many pieces into one result.

Write a simple PHP example using array_reduce to multiply all numbers in an array.

Start with 1 as initial value for multiplication.