Reshaping arrays in MATLAB - Step-by-Step Execution

Concept Flow - Reshaping arrays

Start with original array

↓

Specify new shape dimensions

↓

Check total elements match?

No→Error: Cannot reshape

Yes↓

Rearrange elements into new shape

↓

Output reshaped array

This flow shows how MATLAB reshapes an array by checking if the total number of elements stays the same, then rearranging elements into the new shape.

Execution Sample

MATLAB

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

This code reshapes a 1x6 array into a 2x3 matrix and displays it.

Execution Table

Step	Action	Array Shape	Total Elements	Result / Output
1	Create A	1x6	6	[1 2 3 4 5 6]
2	Specify new shape (2,3)	-	-	-
3	Check total elements match (6 == 2*3)	1x6 and 2x3	6	Match, proceed
4	Reshape A to 2x3	2x3	6	[1 2 3; 4 5 6] (column-wise filling)
5	Display B	2x3	6	1 3 5 2 4 6

💡 Execution stops after displaying reshaped array B.

Variable Tracker

Variable	Start	After Step 1	After Step 4	Final
A	undefined	[1 2 3 4 5 6]	[1 2 3 4 5 6]	[1 2 3 4 5 6]
B	undefined	undefined	[1 2 3; 4 5 6]	[1 2 3; 4 5 6]

Key Moments - 3 Insights

Why does MATLAB fill the reshaped array column-wise, not row-wise?

MATLAB stores arrays in column-major order, so reshape fills elements down columns first, as shown in step 4 of the execution_table.

What happens if the total elements don't match when reshaping?

MATLAB throws an error because the reshape function requires the total number of elements to stay the same, as checked in step 3.

Does reshape change the original array A?

No, reshape creates a new array B with the new shape; A remains unchanged, as seen in variable_tracker.

Visual Quiz - 3 Questions

Look at the execution_table at step 4, what is the value of B(2,1)?

A 3

B 4

C 2

D 5

💡 Hint

Check the reshaped array values in step 4 of execution_table.

At which step does MATLAB verify if the reshape is possible?

A Step 2

B Step 4

C Step 3

D Step 5

💡 Hint

Look for the step where total elements are compared in execution_table.

If A had 8 elements instead of 6, what would happen at step 3?

A Error because total elements don't match

B Reshape proceeds normally

C Array B becomes larger

D Original array A changes shape

💡 Hint

Refer to the explanation in key_moments about element count matching.

Concept Snapshot

reshape(array, rows, cols)
- Changes array shape without changing data order
- Total elements must match (rows*cols = numel(array))
- MATLAB fills reshaped array column-wise
- Original array stays unchanged
- Errors if sizes mismatch

Full Transcript

This visual trace shows how MATLAB reshapes arrays. First, the original array A is created with 6 elements. Then, the new shape 2 rows by 3 columns is specified. MATLAB checks if the total elements match (6 == 2*3). Since they match, it rearranges elements column-wise into the new 2x3 array B. The original array A remains unchanged. The reshaped array B is displayed with elements filled down columns. If the total elements did not match, MATLAB would give an error. This process helps change how data is organized without changing the data itself.