Array map function in PHP - Step-by-Step Execution

Concept Flow - Array map function

Start with array

↓

Pick first element

↓

Apply callback function

↓

Store result in new array

↓

More elements?

Yes→Pick next element

No↓

Return new array

The map function takes each element of an array, applies a function to it, and collects the results into a new array.

Execution Sample

PHP

<?php
$numbers = [1, 2, 3];
$squares = array_map(fn($n) => $n * $n, $numbers);
print_r($squares);
?>

This code squares each number in the array and prints the new array.

Execution Table

Step	Current Element	Callback Applied	Result Stored	New Array State
1	1	1 * 1 = 1	1	[1]
2	2	2 * 2 = 4	4	[1, 4]
3	3	3 * 3 = 9	9	[1, 4, 9]
4	No more elements	-	-	[1, 4, 9]

💡 All elements processed, map returns new array [1, 4, 9]

Variable Tracker

Variable	Start	After 1	After 2	After 3	Final
numbers	[1, 2, 3]	[1, 2, 3]	[1, 2, 3]	[1, 2, 3]	[1, 2, 3]
current element	N/A	1	2	3	N/A
result	N/A	1	4	9	N/A
squares	[]	[1]	[1, 4]	[1, 4, 9]	[1, 4, 9]

Key Moments - 2 Insights

Why does the original array 'numbers' not change after using array_map?

array_map creates a new array with the results and does not modify the original array, as shown in the variable_tracker where 'numbers' stays the same.

What happens if the callback function returns a different type than the input?

The new array will contain the returned values exactly as produced by the callback, regardless of type, because array_map stores the callback results directly.

Visual Quiz - 3 Questions

Look at the execution_table, what is the 'Result Stored' at step 2?

A 2

B 4

C 1

D 9

💡 Hint

Check the 'Result Stored' column in row 2 of the execution_table.

At which step does the map function finish processing all elements?

A Step 4

B Step 3

C Step 2

D Step 1

💡 Hint

Look for the step where 'No more elements' appears in the 'Current Element' column.

If the callback function was changed to return $n + 1, what would be the 'New Array State' after step 3?

A [1, 2, 3]

B [1, 4, 9]

C [2, 3, 4]

D [0, 1, 2]

💡 Hint

Consider how adding 1 to each element changes the array values in the variable_tracker.

Concept Snapshot

array_map(callback, array) applies callback to each element
Returns a new array with results
Original array stays unchanged
Callback can be any function or closure
Useful for transforming arrays easily

Full Transcript

The PHP array_map function takes an array and a callback function. It applies the callback to each element in the array one by one. Each result is stored in a new array. The original array remains unchanged. After all elements are processed, the new array is returned. For example, squaring each number in [1, 2, 3] produces [1, 4, 9]. This process is stepwise: pick element, apply function, store result, repeat until done.