MATLAB file I/O (loadmat, savemat) in SciPy - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to load a MATLAB file named 'data.mat' into a Python variable.

SciPy

from scipy.io import [1]
data = [1]('data.mat')

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

Areadmat

Bsavemat

Cloadmat

Dloadtxt

Attempts:

3 left

💡 Hint

Common Mistakes

Using savemat instead of loadmat

Trying to use loadtxt which is for text files

The loadmat function from scipy.io loads MATLAB files into Python.

2fill in blank

medium

Complete the code to save a Python dictionary 'my_data' to a MATLAB file named 'output.mat'.

SciPy

from scipy.io import [1]
my_data = {'a': [1, 2, 3]}
[1]('output.mat', my_data)

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

Aloadmat

Bdumpmat

Csave

Dsavemat

Attempts:

3 left

💡 Hint

Common Mistakes

Using loadmat instead of savemat

Using save which is not a scipy.io function

The savemat function saves Python data to a MATLAB .mat file.

3fill in blank

hard

Fix the error in the code to correctly load a MATLAB file and access variable 'x'.

SciPy

from scipy.io import loadmat
data = loadmat('file.mat')
x = data[1]

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

A['x']

Bx

C.x

D['data']

Attempts:

3 left

💡 Hint

Common Mistakes

Trying to access variable as an attribute with dot notation

Using variable name without quotes or brackets

MATLAB variables are accessed from the loaded dictionary using square brackets and the variable name as a string.

4fill in blank

hard

Fill both blanks to save a dictionary with variable 'y' to 'result.mat' and then load it back.

SciPy

from scipy.io import [1], [2]
data_to_save = {'y': [4, 5, 6]}
[1]('result.mat', data_to_save)
loaded_data = [2]('result.mat')

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

Asavemat

Bloadmat

Csave

Dreadmat

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up savemat and loadmat

Using non-existing functions like save or readmat

Use savemat to save and loadmat to load MATLAB files.

5fill in blank

hard

Fill all three blanks to load 'data.mat', extract variable 'z', and save it to 'new_data.mat'.

SciPy

from scipy.io import [1], [2]
data = [1]('data.mat')
z = data['z']
[2]('new_data.mat', {'z': z})

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

Aloadmat

Bsavemat

Cload

Dsave

Attempts:

3 left

💡 Hint

Common Mistakes

Using save or load which are not scipy.io functions

Not importing both functions before use

Use loadmat to load and savemat to save MATLAB files.

Practice

1.

What does the scipy.io.loadmat function do?

easy

A. Loads data from a MATLAB .mat file into a Python dictionary

B. Saves a Python dictionary as a MATLAB .mat file

C. Converts Python lists to MATLAB arrays

D. Executes MATLAB code from Python

Solution

1. Step 1: Understand the function purpose

   loadmat is designed to read MATLAB .mat files.

2. Step 2: Identify the output type

   It returns the data as a Python dictionary with variable names as keys.

3. Final Answer:

   Loads data from a MATLAB .mat file into a Python dictionary -> Option A

4. Quick Check:

   loadmat reads .mat files into dict [OK]

Hint: Remember: loadmat reads, savemat writes [OK]

Common Mistakes:

• Confusing loadmat with savemat
• Thinking loadmat executes MATLAB code
• Assuming loadmat converts data formats automatically

2.

Which of the following is the correct way to save a Python dictionary data to a MATLAB file named output.mat using savemat?

?

easy

A. savemat('output.mat', data)

B. savemat(data, 'output.mat')

C. savemat({'output.mat': data})

D. savemat('output.mat', {'data': data})

Solution

1. Step 1: Check savemat function signature

   savemat(filename, dict) requires a filename string and a dictionary of variables.

2. Step 2: Wrap data in a dictionary with a variable name

   To save data, it must be inside another dictionary like {'data': data}.

3. Final Answer:

   savemat('output.mat', {'data': data}) -> Option D

4. Quick Check:

   savemat needs filename and dict [OK]

Hint: savemat needs dict with variable names as keys [OK]

Common Mistakes:

• Passing data directly without wrapping in dict
• Swapping filename and data arguments
• Using incorrect argument types

3.

What will be the output of the following code?

from scipy.io import loadmat
mat_data = loadmat('sample.mat')
print(type(mat_data))

Assume sample.mat is a valid MATLAB file.

medium

A. <class 'numpy.ndarray'>

B. <class 'dict'>

C. <class 'list'>

D. FileNotFoundError

Solution

1. Step 1: Understand loadmat output

   loadmat returns a Python dictionary containing MATLAB variables.

2. Step 2: Check the printed type

   Printing type of mat_data shows <class 'dict'>.

3. Final Answer:

   <class 'dict'> -> Option B

4. Quick Check:

   loadmat returns dict [OK]

Hint: loadmat output is always a dict [OK]

Common Mistakes:

• Expecting a list or array directly
• Assuming loadmat raises error if file exists
• Confusing output type with variable inside dict

4.

Identify the error in this code snippet:

from scipy.io import savemat
my_data = {'x': [1, 2, 3]}
savemat(my_data, 'data.mat')

medium

A. Dictionary keys must be strings

B. List values cannot be saved in .mat files

C. Arguments to savemat are in wrong order

D. Missing import statement

Solution

1. Step 1: Check savemat argument order

   savemat expects filename first, then dictionary.

2. Step 2: Identify argument swap

   Code passes dictionary first, filename second, which is incorrect.

3. Final Answer:

   Arguments to savemat are in wrong order -> Option C

4. Quick Check:

   savemat(filename, dict) order matters [OK]

Hint: Filename is first argument in savemat [OK]

Common Mistakes:

• Swapping filename and data arguments
• Assuming lists can't be saved
• Forgetting to import savemat

5.

You want to save two variables, a = [1, 2, 3] and b = [[4, 5], [6, 7]], into a MATLAB file vars.mat. Which code correctly saves both variables so MATLAB can load them as a and b?

hard

A. savemat('vars.mat', {'a': a, 'b': b})

B. savemat('vars.mat', {'vars': [a, b]})

C. savemat('vars.mat', {'a': [a], 'b': [b]})

D. savemat('vars.mat', {'a': a}, {'b': b})

Solution

1. Step 1: Understand savemat input format

   savemat requires a dictionary mapping variable names to values.

2. Step 2: Check how to save multiple variables

   Pass a single dictionary with keys 'a' and 'b' mapped to their values.

3. Step 3: Identify correct option

   savemat('vars.mat', {'a': a, 'b': b}) correctly passes {'a': a, 'b': b} as one dictionary.

4. Final Answer:

   savemat('vars.mat', {'a': a, 'b': b}) -> Option A

5. Quick Check:

   Multiple variables saved in one dict [OK]

Hint: Use one dict with all variables as keys [OK]

Common Mistakes:

• Passing multiple dicts instead of one
• Wrapping variables in extra lists unnecessarily
• Using a single key for multiple variables