Array chunk and pad in PHP - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the PHP function array_chunk() do?

It splits an array into smaller arrays (chunks) of a specified size. Each chunk is a new array containing elements from the original array.

beginner

How does array_pad() work in PHP?

It adds elements to an array until it reaches a specified size. You can add elements at the end (positive size) or at the beginning (negative size).

intermediate

What happens if the size parameter in array_chunk() is larger than the array length?

The function returns one chunk containing the entire original array because it cannot split into smaller chunks.

intermediate

Can array_pad() shrink an array if the size is smaller than the current array length?

No, array_pad() only adds elements if the array is smaller than the specified size. It does not remove elements.

beginner

Show a simple example of using array_chunk() and array_pad() together.

Example:

$arr = [1, 2, 3, 4];
$chunks = array_chunk($arr, 2); // [[1, 2], [3, 4]]
$padded = array_pad($chunks[0], 4, 0); // [1, 2, 0, 0]

What does array_chunk([1,2,3,4,5], 2) return?

A [[1,2], [3,4], [5]]

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

C [[1,2], [3,4,5]]

D [[1], [2], [3], [4], [5]]

The array is split into chunks of size 2. The last chunk contains the remaining element.

What will array_pad([1,2], 5, 0) return?

A [1, 2, 5]

B [1, 2]

C [0, 0, 1, 2]

D [1, 2, 0, 0, 0]

The array is padded at the end with zeros until it reaches size 5.

If you use array_pad([1,2,3], -5, 'x'), where are the elements added?

A At the end

B At the beginning

C No elements are added

D Elements replace existing ones

A negative size pads the array at the beginning.

What happens if you call array_chunk([1,2,3], 10)?

A [[1,2,3]]

B []

C [[1,2], [3]]

D Error

Since chunk size is larger than array length, the whole array is one chunk.

Does array_pad() remove elements if the array is bigger than the size?

A Yes, it removes extra elements

B It throws an error

C No, it only adds elements

D It duplicates elements

array_pad only adds elements; it never removes them.

Explain how you can split an array into smaller parts and then make sure each part has the same length by adding extra elements.

Think about splitting first, then adding elements to chunks.

Describe the difference between positive and negative size values in array_pad.

Where do new elements go depending on sign of size?

Practice

1. What does the PHP function array_chunk do?

easy

A. Splits an array into smaller arrays of a fixed size

B. Adds elements to the end of an array to reach a certain size

C. Removes duplicate values from an array

D. Sorts an array in ascending order

Solution

1. Step 1: Understand the function purpose

   array_chunk is designed to split a large array into smaller arrays each having a fixed number of elements.

2. Step 2: Compare with other options

   Adding elements to reach a size is done by array_pad, not array_chunk. Removing duplicates or sorting are unrelated functions.

3. Final Answer:

   Splits an array into smaller arrays of a fixed size -> Option A

4. Quick Check:

   array_chunk = split array [OK]

Hint: Remember: chunk means break into pieces [OK]

Common Mistakes:

• Confusing array_chunk with array_pad
• Thinking it sorts or removes duplicates
• Assuming it modifies the original array in place

2. Which of the following is the correct syntax to pad an array $arr to size 5 with the value 0 using array_pad?

easy

A. $padded = array_pad($arr, 5);

B. $padded = array_pad(5, $arr, 0);

C. $padded = array_pad($arr, 5, 0);

D. $padded = array_pad($arr, 0, 5);

Solution

1. Step 1: Recall array_pad syntax

   The correct syntax is array_pad(array, size, value), where the first argument is the array, second is the desired size, third is the padding value.

2. Step 2: Check each option

   $padded = array_pad($arr, 5, 0); matches the correct order and arguments. Options B and C have wrong argument order. $padded = array_pad($arr, 5); misses the padding value.

3. Final Answer:

   $padded = array_pad($arr, 5, 0); -> Option C

4. Quick Check:

   array_pad(array, size, value) correct order [OK]

Hint: Remember: array_pad(array, size, value) [OK]

Common Mistakes:

• Swapping argument order
• Omitting the padding value
• Passing size as first argument

3. What is the output of the following PHP code?

$arr = [1, 2, 3, 4, 5];
$chunks = array_chunk($arr, 2);
print_r($chunks);

medium

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

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

C. [[1, 2], [3, 4], [5, null]]

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

Solution

1. Step 1: Understand array_chunk behavior

   array_chunk splits the array into smaller arrays each with 2 elements, except the last chunk which may have fewer if elements run out.

2. Step 2: Apply to given array

   Splitting [1,2,3,4,5] by 2 gives chunks: [1,2], [3,4], and [5]. No padding is added by array_chunk.

3. Final Answer:

   [[1, 2], [3, 4], [5]] -> Option B

4. Quick Check:

   array_chunk splits into groups of 2 [OK]

Hint: Last chunk may be smaller if not divisible [OK]

Common Mistakes:

• Expecting padding in array_chunk
• Confusing chunk size with number of chunks
• Assuming all chunks have equal length always

4. Identify the error in this PHP code snippet:

$arr = [1, 2];
$padded = array_pad($arr, 5);
print_r($padded);

medium

A. print_r cannot print arrays

B. array_pad cannot increase array size

C. array_pad requires the size to be smaller than original

D. Missing the padding value argument in array_pad

Solution

1. Step 1: Check array_pad function signature

   array_pad requires three arguments: the array, the new size, and the value to pad with.

2. Step 2: Identify missing argument

   The code calls array_pad with only two arguments, missing the padding value, which causes an error.

3. Final Answer:

   Missing the padding value argument in array_pad -> Option D

4. Quick Check:

   array_pad needs 3 arguments [OK]

Hint: array_pad needs array, size, and value [OK]

Common Mistakes:

• Forgetting the padding value
• Assuming array_pad works with two arguments
• Thinking print_r can't print arrays

5. You have an array $data = [10, 20, 30]. You want to split it into chunks of size 2 and ensure each chunk has exactly 2 elements by padding with 0 if needed. Which code correctly achieves this?

hard

A. $chunks = array_chunk($data, 2);
foreach ($chunks as &$chunk) {
$chunk = array_pad($chunk, 2, 0);
}
print_r($chunks);

B. $chunks = array_pad(array_chunk($data, 2), 2, 0);
print_r($chunks);

C. $chunks = array_chunk(array_pad($data, 5, 0), 2);
print_r($chunks);

D. $chunks = array_chunk($data, 2, 0);
print_r($chunks);

Solution

1. Step 1: Understand the goal

   We want chunks of size 2, each chunk exactly length 2, padding with 0 if chunk is smaller.

2. Step 2: Analyze each option

   $chunks = array_chunk($data, 2); foreach ($chunks as &$chunk) { $chunk = array_pad($chunk, 2, 0); } print_r($chunks); splits into chunks, then pads each chunk to size 2 with 0, which is correct.
   $chunks = array_pad(array_chunk($data, 2), 2, 0); print_r($chunks); tries to pad the array of chunks, which is incorrect.
   $chunks = array_chunk(array_pad($data, 5, 0), 2); print_r($chunks); pads the original array to size 5, then chunks, which may add unwanted extra elements.
   $chunks = array_chunk($data, 2, 0); print_r($chunks); passes 0 as third argument to array_chunk, which is invalid.

3. Final Answer:

   $chunks = array_chunk($data, 2); foreach ($chunks as &$chunk) { $chunk = array_pad($chunk, 2, 0); } print_r($chunks); -> Option A

4. Quick Check:

   Pad each chunk after chunking [OK]

Hint: Pad each chunk after chunking, not the whole array [OK]

Common Mistakes:

• Padding the whole array before chunking
• Passing extra arguments to array_chunk
• Trying to pad the array of chunks directly