transpose() for swapping axes in NumPy - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to transpose the 2D array using numpy.

NumPy

import numpy as np
arr = np.array([[1, 2], [3, 4]])
transposed = arr.[1]()

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

Atranspose

Bswapaxes

Creshape

Dflatten

Attempts:

3 left

💡 Hint

Common Mistakes

Using reshape instead of transpose changes the shape but not the axes.

Using flatten converts the array to 1D, not transposing it.

The transpose() method swaps the axes of the array, turning rows into columns.

2fill in blank

medium

Complete the code to transpose a 3D numpy array by swapping the first and second axes.

NumPy

import numpy as np
arr = np.random.rand(2, 3, 4)
transposed = arr.transpose([1])

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

A(0, 1, 2)

B(1, 0, 2)

C(2, 1, 0)

D(0, 2, 1)

Attempts:

3 left

💡 Hint

Common Mistakes

Using (0, 1, 2) does not change axes order.

Using (2, 1, 0) reverses all axes, not just the first two.

To swap the first and second axes, use transpose((1, 0, 2)).

3fill in blank

hard

Fix the error in the code to correctly transpose the 2D numpy array.

NumPy

import numpy as np
arr = np.array([[5, 6], [7, 8]])
transposed = arr.[1]

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

Atranspose

Btranspose{}

Ctranspose[]

Dtranspose()

Attempts:

3 left

💡 Hint

Common Mistakes

Forgetting parentheses causes no transposition.

Using brackets or braces instead of parentheses causes syntax errors.

The transpose method must be called with parentheses () to execute it.

4fill in blank

hard

Fill both blanks to create a dictionary with words as keys and their lengths as values, but only for words longer than 3 characters.

NumPy

words = ['data', 'is', 'fun', 'and', 'cool']
lengths = {word: [1] for word in words if len(word) [2] 3}

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

Alen(word)

B>

C<

Dword

Attempts:

3 left

💡 Hint

Common Mistakes

Using < instead of > filters out the wrong words.

Using word instead of len(word) stores the word, not its length.

The dictionary comprehension uses len(word) for values and filters words with length greater than 3 using >.

5fill in blank

hard

Fill all three blanks to create a dictionary with uppercase words as keys and their lengths as values, only for words longer than 3 characters.

NumPy

words = ['data', 'is', 'fun', 'and', 'cool']
result = [1]: [2] for w in words if len(w) [3] 3}}

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

Aw.upper()

Blen(w)

C>

Dw

Attempts:

3 left

💡 Hint

Common Mistakes

Using w instead of w.upper() stores lowercase keys.

Using < instead of > filters the wrong words.

The dictionary comprehension uses w.upper() as keys, len(w) as values, and filters words with length greater than 3 using >.

Practice

1. What does the numpy.transpose() function do to an array?

easy

A. It removes duplicate elements from the array.

B. It adds new elements to the array.

C. It sorts the array elements in ascending order.

D. It swaps or flips the axes of the array.

Solution

1. Step 1: Understand the purpose of transpose()

   The transpose() function changes the order of axes in an array, effectively flipping or swapping them.

2. Step 2: Compare with other options

   Adding elements, sorting, or removing duplicates are unrelated to axis swapping.

3. Final Answer:

   It swaps or flips the axes of the array. -> Option D

4. Quick Check:

   transpose() = swaps axes [OK]

Hint: Remember: transpose flips axes, not values or elements [OK]

Common Mistakes:

• Thinking transpose sorts or changes values
• Confusing transpose with adding or removing elements
• Assuming transpose only works on 2D arrays

2. Which of the following is the correct syntax to transpose a 2D NumPy array named arr?

easy

A. transpose(arr)

B. arr.transpose

C. arr.transpose()

D. arr.transpose[]

Solution

1. Step 1: Recall method call syntax in Python

   To call a method, parentheses are required: arr.transpose().

2. Step 2: Check other options

   transpose(arr) is incorrect because transpose is a method, not a standalone function here; arr.transpose misses parentheses; arr.transpose[] is invalid syntax.

3. Final Answer:

   arr.transpose() -> Option C

4. Quick Check:

   Method call needs parentheses [OK]

Hint: Use parentheses to call transpose method: arr.transpose() [OK]

Common Mistakes:

• Omitting parentheses when calling transpose
• Using transpose as a standalone function without import
• Using invalid syntax like brackets after method

3. What is the output of the following code?

import numpy as np
arr = np.array([[1, 2, 3], [4, 5, 6]])
print(arr.transpose())

medium

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

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

C. [[1 4 2]
[3 5 6]]

D. [[6 5 4]
[3 2 1]]

Solution

1. Step 1: Understand the original array shape

   The array has shape (2, 3): 2 rows and 3 columns.

2. Step 2: Apply transpose()

   Transpose swaps axes, so shape becomes (3, 2). Rows become columns and vice versa. The first column becomes the first row: [1,4], second: [2,5], third: [3,6].

3. Final Answer:

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

4. Quick Check:

   Transpose swaps rows and columns [OK]

Hint: Transpose flips rows and columns in 2D arrays [OK]

Common Mistakes:

• Confusing transpose with reversing elements
• Expecting original shape after transpose
• Mixing up rows and columns in output

4. The following code throws an error. What is the mistake?

import numpy as np
arr = np.array([[[1,2],[3,4]], [[5,6],[7,8]]])
print(arr.transpose(1, 0))

medium

A. transpose() requires all axes to be specified for 3D arrays.

B. The array is not a NumPy array.

C. transpose() cannot be used on 3D arrays.

D. The axes argument must be a list, not a tuple.

Solution

1. Step 1: Check array dimensions

   The array has 3 dimensions (shape (2, 2, 2)).

2. Step 2: Understand transpose axes argument

   For 3D arrays, transpose requires all three axes to be specified. Passing only two axes (1, 0) causes an error.

3. Final Answer:

   transpose() requires all axes to be specified for 3D arrays. -> Option A

4. Quick Check:

   All axes must be given for 3D transpose [OK]

Hint: Specify all axes when transposing multi-dimensional arrays [OK]

Common Mistakes:

• Passing fewer axes than array dimensions
• Thinking transpose can't handle 3D arrays
• Confusing tuple and list for axes argument

5. Given a 3D NumPy array arr with shape (2, 3, 4), which transpose() call will swap the first and last axes, resulting in shape (4, 3, 2)?

hard

A. arr.transpose(2, 0, 1)

B. arr.transpose(2, 1, 0)

C. arr.transpose(0, 2, 1)

D. arr.transpose(1, 0, 2)

Solution

1. Step 1: Identify original axes order

   Original shape (2, 3, 4) corresponds to axes (0, 1, 2).

2. Step 2: Determine desired axes order

   Swapping first and last axes means new order is (2, 1, 0), resulting in shape (4, 3, 2).

3. Final Answer:

   arr.transpose(2, 1, 0) -> Option B

4. Quick Check:

   Swap axes 0 and 2: (2,1,0) [OK]

Hint: List axes in desired order to swap them correctly [OK]

Common Mistakes:

• Mixing up axes order in transpose
• Not specifying all axes for 3D arrays
• Assuming transpose swaps only two axes automatically