Reshaping arrays in MATLAB - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to reshape the vector into a 2x3 matrix.

MATLAB

A = 1:6;
B = reshape(A, [1]);

Drag options to blanks, or click blank then click option'

A[2, 3]

B[3, 2]

C[6, 1]

D[1, 6]

Attempts:

3 left

💡 Hint

Common Mistakes

Using dimensions that do not multiply to the total number of elements.

Swapping rows and columns.

The reshape function changes the shape of the array. Here, we want a 2 rows and 3 columns matrix, so use [2, 3].

2fill in blank

medium

Complete the code to reshape matrix M into a column vector.

MATLAB

M = [1 2 3; 4 5 6];
V = reshape(M, [1]);

Drag options to blanks, or click blank then click option'

A[6, 1]

B[3, 2]

C[1, 6]

D[2, 3]

Attempts:

3 left

💡 Hint

Common Mistakes

Using [1, 6] which creates a row vector instead.

Confusing rows and columns.

To reshape M into a column vector, it must have 6 rows and 1 column, so use [6, 1].

3fill in blank

hard

Fix the error in reshaping matrix X into a 3x3 matrix.

MATLAB

X = 1:8;
Y = reshape(X, [1]);

Drag options to blanks, or click blank then click option'

A[3, 3]

B[2, 4]

C[1, 8]

D[4, 2]

Attempts:

3 left

💡 Hint

Common Mistakes

Trying to reshape into a size that does not match the number of elements.

Ignoring the error message from MATLAB.

The vector X has 8 elements, so it cannot be reshaped into a 3x3 matrix (which needs 9 elements). Using [1, 8] keeps it as a row vector.

4fill in blank

hard

Fill both blanks to reshape vector V into a 4x2 matrix and then back to a 2x4 matrix.

MATLAB

V = 1:8;
M1 = reshape(V, [1]);
M2 = reshape(M1, [2]);

Drag options to blanks, or click blank then click option'

A[4, 2]

B[2, 4]

C[8, 1]

D[1, 8]

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up the order of rows and columns.

Using incompatible dimensions that don't match the number of elements.

First reshape V into 4 rows and 2 columns, then reshape M1 into 2 rows and 4 columns.

5fill in blank

hard

Fill all three blanks to create a 3D array from vector W and then reshape it back to a 2D matrix.

MATLAB

W = 1:12;
A = reshape(W, [1], [2], [3]);
B = reshape(A, [4, 3]);

Drag options to blanks, or click blank then click option'

A2

B3

D6

Attempts:

3 left

💡 Hint

Common Mistakes

Choosing dimensions that do not multiply to 12.

Confusing the order of dimensions.

The vector W has 12 elements. Reshape it into a 3D array with dimensions 2x3x2 (2*3*2=12). Then reshape back to a 4x3 matrix.

Practice

1. What does the MATLAB function reshape do to an array?

easy

A. Sorts the array elements in ascending order

B. Changes the data values but keeps the shape the same

C. Deletes elements from the array

D. Changes the shape of the array without changing its data

Solution

1. Step 1: Understand the purpose of reshape

   The reshape function changes how the array is organized in terms of rows and columns but does not modify the actual data values.

2. Step 2: Confirm data remains unchanged

   The total number of elements stays the same, so no data is lost or changed, only rearranged.

3. Final Answer:

   Changes the shape of the array without changing its data -> Option D

4. Quick Check:

   reshape changes shape, not data [OK]

Hint: Remember reshape only rearranges elements, data stays same [OK]

Common Mistakes:

• Thinking reshape changes data values
• Assuming reshape deletes elements
• Confusing reshape with sorting

2. Which of the following is the correct syntax to reshape a 1x6 vector A into a 2x3 matrix in MATLAB?

easy

A. reshape(A, 2, 3)

B. reshape(2, 3, A)

C. reshape(A, [3 2])

D. reshape(A, 3, 2)

Solution

1. Step 1: Recall reshape syntax

   The correct syntax is reshape(array, rows, columns). So the array comes first, then the new dimensions.

2. Step 2: Check dimensions for 2x3

   To reshape into 2 rows and 3 columns, use reshape(A, 2, 3). Options with swapped dimensions or wrong order are incorrect.

3. Final Answer:

   reshape(A, 2, 3) -> Option A

4. Quick Check:

   reshape(array, rows, cols) [OK]

Hint: Syntax is reshape(array, rows, columns) [OK]

Common Mistakes:

• Putting dimensions before the array
• Swapping rows and columns
• Using brackets incorrectly

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

A = 1:6;
B = reshape(A, 3, 2);
disp(B);

medium

A. [1 4; 2 5; 3 6]

B. [1 2; 3 4; 5 6]

C. [1 3 5; 2 4 6]

D. [1 2 3; 4 5 6]

Solution

1. Step 1: Understand reshape fills column-wise

   MATLAB fills the reshaped matrix column by column from the original vector. The vector A = [1 2 3 4 5 6].

2. Step 2: Fill 3 rows and 2 columns

   Fill first column: 1, 2, 3; second column: 4, 5, 6. So matrix B is:
   [1 4;
   2 5;
   3 6]

3. Final Answer:

   [1 4; 2 5; 3 6] -> Option A

4. Quick Check:

   reshape fills column-wise [OK]

Hint: Remember MATLAB fills columns first in reshape [OK]

Common Mistakes:

• Assuming row-wise filling
• Mixing up rows and columns
• Confusing output format

4. Identify the error in this MATLAB code:

A = 1:8;
B = reshape(A, 3, 3);

medium

A. Variable A is not defined correctly

B. reshape dimensions do not match number of elements

C. Syntax error in reshape function

D. No error, code runs fine

Solution

1. Step 1: Count elements in A

   Vector A has 8 elements (1 to 8).

2. Step 2: Check reshape target size

   reshape tries to make a 3x3 matrix which needs 9 elements, but A has only 8.

3. Final Answer:

   reshape dimensions do not match number of elements -> Option B

4. Quick Check:

   Elements must match reshape size [OK]

Hint: Check total elements before reshaping [OK]

Common Mistakes:

• Ignoring element count mismatch
• Assuming reshape pads missing elements
• Thinking reshape auto adjusts size

5. Given a 3D array A of size 2x3x4, which MATLAB command correctly reshapes it into a 6x4 matrix without changing the order of elements?

hard

A. reshape(A, [2 3 4])

B. reshape(A, 4, 6)

C. reshape(A, [6 4])

D. reshape(A, [4 6])

Solution

1. Step 1: Calculate total elements

   Original size is 2x3x4 = 24 elements total.

2. Step 2: Confirm reshape size matches total elements

   6x4 = 24 elements, so reshape to [6 4] is valid.

3. Step 3: Use correct syntax for reshape with vector size

   reshape accepts size as a vector, so reshape(A, [6 4]) is correct and clearer for multi-dimensional arrays.

4. Final Answer:

   reshape(A, [6 4]) -> Option C

5. Quick Check:

   Use vector size for multi-dim reshape [OK]

Hint: Use reshape(A, [rows cols]) for multi-dim arrays [OK]

Common Mistakes:

• Swapping rows and columns
• Using wrong syntax without brackets
• Ignoring total element count