2D array indexing (row, col) in NumPy - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to access the element in the 2D array at row 1, column 2.

NumPy

import numpy as np
arr = np.array([[10, 20, 30], [40, 50, 60]])
element = arr[[1]]
print(element)

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A1, 2

Attempts:

3 left

💡 Hint

Common Mistakes

Using arr[1][2] instead of arr[1, 2]

Using one index instead of two

Mixing up row and column indices

To access an element in a 2D numpy array, use arr[row, column]. Here, row 1 and column 2 gives the element 60.

2fill in blank

medium

Complete the code to extract the entire second row from the 2D array.

NumPy

import numpy as np
arr = np.array([[5, 10, 15], [20, 25, 30], [35, 40, 45]])
row = arr[[1]]
print(row)

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A0

B2

C1

D3

Attempts:

3 left

💡 Hint

Common Mistakes

Using index 2 to get the second row

Using arr[:, 1] which gets the second column

Using negative indices incorrectly

Rows are indexed starting at 0. The second row is at index 1.

3fill in blank

hard

Fix the error in the code to correctly access the element at row 0, column 1.

NumPy

import numpy as np
arr = np.array([[7, 8, 9], [10, 11, 12]])
element = arr[[1]]
print(element)

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A[0, 1]

B0, 1

C0][1

D0;1

Attempts:

3 left

💡 Hint

Common Mistakes

Using multiple square brackets like arr[0][1]

Using a list inside brackets like arr[[0,1]]

Using semicolon instead of comma

Use comma-separated indices inside square brackets to access elements in numpy arrays: arr[0, 1].

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 = ['cat', 'house', 'dog', 'elephant']
lengths = {word: [1] for word in words if [2]
print(lengths)

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Alen(word)

Blen(word) > 3

Cword > 3

Dword.length > 3

Attempts:

3 left

💡 Hint

Common Mistakes

Comparing the word string directly to a number

Using incorrect attribute like word.length

Not filtering words at all

Use len(word) to get the length, and filter words with length greater than 3 using len(word) > 3.

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 4 characters.

NumPy

words = ['apple', 'bat', 'carrot', 'dog']
result = { [1]: [2] for w in words if [3] }
print(result)

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Aw.upper()

Blen(w)

Clen(w) > 4

Dw.lower()

Attempts:

3 left

💡 Hint

Common Mistakes

Using lowercase instead of uppercase for keys

Not filtering words by length

Mixing up keys and values in the dictionary comprehension

Use w.upper() for keys, len(w) for values, and filter words with length greater than 4 using len(w) > 4.