Data Science with Python NumPy Array Manipulation Questions and Answers

Question 1

A data scientist has a 2D NumPy array representing daily sales data for 4 products over 6 days, with a shape of (6, 4).
They need to transform this array so that each row represents a product and each column represents a day.
Which of the following NumPy operations will correctly perform this transformation?

Accepted Answer

np.transpose(arr)

Answer

arr.reshape(4, 6)

Answer

np.ravel(arr)

Answer

np.vsplit(arr, 2)

Question 2

You are given two 1D NumPy arrays, `a1 = np.array([1, 2, 3])` and `a2 = np.array([4, 5, 6])`. Which function would you use to combine them into a single 2D array where `a1` is the first row and `a2` is the second row?

Accepted Answer

np.vstack((a1, a2))

Answer

np.hstack((a1, a2))

Answer

np.concatenate((a1, a2), axis=1)

Answer

np.column_stack((a1, a2))

Question 3

What is the key difference between NumPy's `ravel()` and `flatten()` methods when used to convert a multi-dimensional array into a 1D array?

Accepted Answer

`ravel()` returns a view of the original array whenever possible, while `flatten()` always returns a new copy.

Answer

`ravel()` always returns a copy, while `flatten()` returns a view.

Answer

`flatten()` can only be used on 2D arrays, while `ravel()` works on any dimension.

Answer

There is no functional difference; they are aliases for the same operation.

Question 4

A developer needs to split a NumPy array of shape (8, 10) into 4 equal sub-arrays along its rows. However, if the array cannot be split equally, the program should still proceed without raising an error. Which function is most suitable for this task?

Accepted Answer

np.array_split()

Answer

np.hsplit()

Answer

np.split()

Answer

np.vsplit()

Question 5

Given the code snippet below, what will be the value of the original array `arr` after the final line is executed?

```python
import numpy as np
arr = np.arange(10).reshape(2, 5)
arr.resize(2, 6)
```

Accepted Answer

The `arr` array will be modified in-place to shape (2, 6), with the new elements being repeated values from the original array.

Answer

An error will be thrown because the new size is different.

Answer

A new array will be returned, and `arr` will remain unchanged.

Answer

The `arr` array will be modified in-place to shape (2, 6), with the new elements being zeros.

Question 6

Which of the following statements correctly describes the behavior of `np.hstack()`?

Accepted Answer

It stacks arrays in sequence horizontally (column-wise).

Answer

It joins a sequence of arrays along a new axis.

Answer

It splits an array into multiple sub-arrays horizontally.

Answer

It stacks arrays in sequence vertically (row-wise).