Array slice and splice in PHP

Introduction

Array slice and splice help you take parts of an array or change it by adding or removing items.

You want to get a smaller part of a big list without changing the original.

You need to remove some items from a list and keep the rest.

You want to add new items inside a list at a specific place.

You want to replace some items in a list with new ones.

You want to copy a list or part of it to use somewhere else.

Syntax

PHP

<?php
// Array slice syntax
$sliced_array = array_slice(array $array, int $offset, ?int $length = null, bool $preserve_keys = false);

// Array splice syntax
$removed_elements = array_splice(array &$array, int $offset, ?int $length = null, mixed $replacement = []);
?>

array_slice returns a new array and does not change the original array.

array_splice changes the original array by removing and optionally adding elements.

Examples

This takes 2 items starting from index 1 ('banana' and 'cherry'). The original array stays the same.

PHP

<?php
// Example 1: Slice part of an array
$fruits = ['apple', 'banana', 'cherry', 'date'];
$sliced = array_slice($fruits, 1, 2);
print_r($sliced);

This takes all items from index 2 to the end (30, 40).

PHP

<?php
// Example 2: Slice with offset only
$numbers = [10, 20, 30, 40];
$sliced = array_slice($numbers, 2);
print_r($sliced);

This removes 2 items starting at index 1 ('green', 'blue') from the original array.

PHP

<?php
// Example 3: Splice to remove elements
$colors = ['red', 'green', 'blue', 'yellow'];
$removed = array_splice($colors, 1, 2);
print_r($colors);
print_r($removed);

This replaces 'b' and 'c' with 'x' and 'y' in the original array.

PHP

<?php
// Example 4: Splice to replace elements
$letters = ['a', 'b', 'c', 'd'];
array_splice($letters, 1, 2, ['x', 'y']);
print_r($letters);

Sample Program

This program shows how array_slice returns a new part without changing the original array. Then it shows how array_splice removes some elements and adds new ones, changing the original array.

PHP

<?php
// Create an array
$animals = ['cat', 'dog', 'bird', 'fish', 'horse'];

// Print original array
echo "Original array:\n";
print_r($animals);

// Use array_slice to get a part without changing original
$sliced_animals = array_slice($animals, 1, 3);
echo "\nSliced array (index 1 to 3):\n";
print_r($sliced_animals);

echo "\nArray after slice (unchanged):\n";
print_r($animals);

// Use array_splice to remove and replace elements
$removed_animals = array_splice($animals, 2, 2, ['lion', 'tiger']);
echo "\nRemoved elements by splice:\n";
print_r($removed_animals);

echo "\nArray after splice (changed):\n";
print_r($animals);
?>

Important Notes

Time complexity: array_slice is O(n) where n is the length of the slice; array_splice is O(m) where m is the number of elements removed or added.

Space complexity: array_slice creates a new array, so it uses extra space; array_splice modifies in place, so uses less extra space.

Common mistake: Expecting array_splice to return the changed array. It returns the removed elements instead.

Use array_slice when you want a copy of part of the array without changing the original. Use array_splice when you want to change the original array by removing or adding items.

Summary

array_slice returns a new array with selected elements and does not change the original.

array_splice removes and/or adds elements in the original array and returns the removed elements.

Use slice to copy parts, splice to change the array.

Practice

1. What is the main difference between array_slice and array_splice in PHP?

easy

A. array_slice returns a new array without changing the original, while array_splice modifies the original array.

B. array_slice modifies the original array, while array_splice returns a new array without changes.

C. Both functions modify the original array but in different ways.

D. Both functions return a new array and do not modify the original array.

Solution

1. Step 1: Understand array_slice behavior

   array_slice extracts a portion of the array and returns it as a new array without changing the original array.

2. Step 2: Understand array_splice behavior

   array_splice removes or replaces elements in the original array and returns the removed elements, thus modifying the original array.

3. Final Answer:

   array_slice returns a new array without changing the original, while array_splice modifies the original array. -> Option A

4. Quick Check:

   Slice copies, splice changes original [OK]

Hint: Slice copies array parts, splice changes the original array [OK]

Common Mistakes:

• Thinking both functions modify the original array
• Confusing which function returns a new array
• Assuming splice returns the modified array instead of removed elements

2. Which of the following is the correct syntax to remove 2 elements starting from index 1 using array_splice on array $arr?

easy

A. array_splice($arr, 2, 1);

B. array_splice($arr, 1);

C. array_splice($arr, 1, 2);

D. array_splice($arr, 0, 2);

Solution

1. Step 1: Identify parameters of array_splice

   The function signature is array_splice(array &$array, int $offset, int $length = ?). To remove 2 elements starting at index 1, offset = 1 and length = 2.

2. Step 2: Match parameters to options

   array_splice($arr, 1, 2); uses array_splice($arr, 1, 2); which correctly removes 2 elements starting from index 1.

3. Final Answer:

   array_splice($arr, 1, 2); -> Option C

4. Quick Check:

   Offset 1, length 2 removes correct elements [OK]

Hint: array_splice($arr, start, length) removes elements from start [OK]

Common Mistakes:

• Swapping offset and length values
• Omitting length parameter and removing all after offset
• Using wrong index for offset

3. What will be the output of the following PHP code?

$arr = [10, 20, 30, 40, 50];
$result = array_slice($arr, 2, 2);
print_r($result);

medium

A. [30, 40]

B. [20, 30]

C. [40, 50]

D. [10, 20]

Solution

1. Step 1: Understand array_slice parameters

   It extracts elements starting at index 2, taking 2 elements from $arr.

2. Step 2: Extract elements from the array

   Index 2 is 30, next element is 40, so the slice is [30, 40].

3. Final Answer:

   [30, 40] -> Option A

4. Quick Check:

   Slice from index 2, length 2 = [30, 40] [OK]

Hint: array_slice returns a new array from offset with given length [OK]

Common Mistakes:

• Confusing index start point
• Assuming original array is changed
• Mixing up array_slice with array_splice

4. Consider this code snippet:

$arr = [1, 2, 3, 4, 5];
array_splice($arr, 2, 2, [8, 9]);
print_r($arr);

What is the output?

medium

A. [1, 2, 3, 4, 8, 9, 5]

B. [1, 2, 3, 4, 5]

C. [8, 9, 5]

D. [1, 2, 8, 9, 5]

Solution

1. Step 1: Understand array_splice with replacement

   The call removes 2 elements starting at index 2 (elements 3 and 4) and inserts [8, 9] at that position.

2. Step 2: Modify the original array accordingly

   Original array: [1, 2, 3, 4, 5]
   Remove elements at index 2 and 3: [3, 4]
   Insert [8, 9] at index 2
   Resulting array: [1, 2, 8, 9, 5]

3. Final Answer:

   [1, 2, 8, 9, 5] -> Option D

4. Quick Check:

   Splice replaces elements with new ones [OK]

Hint: Splice can replace elements by passing replacement array [OK]

Common Mistakes:

• Expecting original array unchanged
• Forgetting splice removes elements before inserting
• Confusing splice insertion with append

5. You have an array $data = [5, 10, 15, 20, 25, 30]. You want to remove the middle two elements and insert 100 and 200 in their place, then get a new array with the last three elements without changing the original array. Which code snippet correctly does this?

hard

A. array_splice($data, 2, 2, [100, 200]);
$copy = array_slice($data, -3);
print_r($copy);

B. $copy = array_slice($data, -3);
array_splice($data, 2, 2, [100, 200]);
print_r($copy);

C. $copy = array_splice($data, -3);
array_splice($data, 2, 2, [100, 200]);
print_r($copy);

D. $copy = array_slice($data, 2, 3);
array_splice($data, 2, 2, [100, 200]);
print_r($copy);

Solution

1. Step 1: Extract last three elements without changing original

   Using array_slice($data, -3) copies last three elements [20, 25, 30] into $copy without modifying $data.

2. Step 2: Modify original array by replacing middle two elements

   array_splice($data, 2, 2, [100, 200]) removes elements at index 2 and 3 (15, 20) and inserts 100 and 200.

3. Step 3: Print the copied array

   Printing $copy shows the last three elements of the original array before modification.

4. Final Answer:

   $copy = array_slice($data, -3); array_splice($data, 2, 2, [100, 200]); print_r($copy); -> Option B

5. Quick Check:

   Slice first to copy, then splice to modify [OK]

Hint: Slice first to copy, then splice to modify original [OK]

Common Mistakes:

• Using splice to copy array (modifies original)
• Modifying array before slicing (copy changes)
• Wrong slice parameters for last elements