Reshaping arrays in MATLAB - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of reshaping a matrix

What is the output of the following MATLAB code?

MATLAB

A = [1 2 3 4 5 6];
B = reshape(A, 2, 3);
disp(B);

A [1 3 5; 2 4 6]

B [1 2; 3 4; 5 6]

C [1 4; 2 5; 3 6]

D [1 2 3; 4 5 6]

💡 Hint

Remember MATLAB fills matrices column-wise when reshaping.

The reshape function fills the new matrix column-wise from the original vector. So the first column is [1;2], second is [3;4], third is [5;6].

❓ Predict Output

intermediate

Reshape with incompatible size

What error does this MATLAB code produce?

MATLAB

A = 1:10;
B = reshape(A, 3, 4);

A Error: Dimensions do not agree.

B Error: Number of elements must not change.

C Error: reshape cannot reshape array of length 10 into 3-by-4 matrix.

D No error, outputs a 3x4 matrix with zeros padded.

💡 Hint

Check if the total number of elements matches the new shape.

reshape requires the total number of elements to remain the same. 10 elements cannot fill a 3x4 (12 elements) matrix.

🧠 Conceptual

advanced

Understanding reshape order

Given a 2x3 matrix M = [1 2 3; 4 5 6], what is the result of reshape(M, 3, 2)?

A [1 5; 2 6; 3 4]

B [1 2 3; 4 5 6]

C [1 3 5; 2 4 6]

D [1 5; 4 3; 2 6]

💡 Hint

reshape reads elements column-wise from the original matrix.

The elements are taken column-wise: [1;4;2;5;3;6] and reshaped into 3 rows and 2 columns.

🔧 Debug

advanced

Fix the reshape dimension mismatch

Why does this code produce an error and how to fix it? A = 1:12; B = reshape(A, 4, 5);

MATLAB

A = 1:12;
B = reshape(A, 4, 5);

A Error because 12 elements cannot fill a 4x5 matrix; fix by changing to reshape(A, 3, 4).

B Error because reshape requires square matrices; fix by using reshape(A, 4, 4).

C No error; outputs a 4x5 matrix with last 8 elements zero-padded.

D Error because A is a row vector; fix by transposing A before reshape.

💡 Hint

Check if the product of dimensions matches the number of elements.

reshape requires the total elements to match. 12 elements cannot fill 20 slots (4x5). Changing to 3x4 matches 12 elements.

🚀 Application

expert

Reshape and transpose combined

What is the output of this MATLAB code?

MATLAB

A = [1 2 3 4 5 6];
B = reshape(A, 2, 3)';
disp(B);

A [1 3 5; 2 4 6]

B [1 2; 3 4; 5 6]

C [1 4; 2 5; 3 6]

D [1 2 3; 4 5 6]

💡 Hint

First reshape fills column-wise, then transpose swaps rows and columns.

reshape(A,2,3) creates a 2x3 matrix filled column-wise: [1 3 5; 2 4 6]. Transpose swaps rows and columns to get [1 2; 3 4; 5 6].