Array slice and splice in PHP - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the array_slice() function do in PHP?

It returns a portion of an array without modifying the original array. You specify the start position and length of the slice.

beginner

How does array_splice() differ from array_slice()?

array_splice() removes a portion of an array and can replace it with new elements. It modifies the original array.

intermediate

What happens if you use a negative start index in array_slice()?

The slice starts that many elements from the end of the array. For example, -2 means start from the second last element.

intermediate

What does array_splice($array, 2, 3, ['a', 'b']) do?

It removes 3 elements from $array starting at index 2, then inserts 'a' and 'b' at that position, modifying $array.

intermediate

Does array_slice() preserve keys by default?

No, by default it reindexes the returned array starting from 0. You can preserve keys by passing true as the fourth argument.

Which function modifies the original array in PHP?

A array_map()

B array_slice()

C array_merge()

D array_splice()

array_splice() changes the original array by removing and optionally replacing elements.

What does array_slice($arr, 1, 2) return?

A Two elements starting from index 1

B Elements from index 1 to 2 inclusive

C All elements except the first

D The entire array

It returns 2 elements starting at index 1, without modifying the original array.

How do you preserve keys when using array_slice()?

A Pass true as the fourth argument

B Pass false as the third argument

C Use array_splice() instead

D Keys are always preserved

Passing true as the fourth argument preserves the original keys in the returned slice.

What does array_splice($arr, 0, 0, ['x']) do?

A Removes the first element

B Inserts 'x' at the start without removing elements

C Replaces the first element with 'x'

D Returns an empty array

It inserts 'x' at the start without removing any elements because length is 0.

If you want to get the last 3 elements of an array without changing it, which is best?

A array_splice($arr, -3)

B array_shift() three times

C array_slice($arr, -3)

D array_pop() three times

array_slice($arr, -3) returns the last 3 elements without modifying the original array.

Explain the difference between array_slice() and array_splice() in PHP.

Think about whether the original array changes or not.

Describe how to use array_splice() to remove elements and insert new ones.

Remember it works like cutting out and pasting in new pieces.

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