100 numpy questions

Question 1

How to import the numpy package under the name np?

Answer 1

import numpy as np

Question 2

How to print the numpy version and the configuration?

Answer 2

print(np.\_\_version\_\_) and np.show_config()

Question 3

How to create a null vector of size 10?

Answer 3

Z = np.zeros(10)

Question 4

How to find the memory size of any array?

Answer 4

Z.size * Z.itemsize (e.g., print(\"%d bytes\" % (Z.size * Z.itemsize)))

Question 5

How to get the documentation of the numpy add function from the command line?

Answer 5

%run python -c \"import numpy; numpy.info(numpy.add)\"

Question 6

How to create a null vector of size 10 with the fifth value as 1?

Answer 6

Z = np.zeros(10); Z[4] = 1

Question 7

How to create a vector with values ranging from 10 to 49?

Answer 7

Z = np.arange(10, 50)

Question 8

How to reverse a vector (first element becomes last)?

Answer 8

Z = Z[::-1]

Question 9

How to create a 3x3 matrix with values ranging from 0 to 8?

Answer 9

Z = np.arange(9).reshape(3, 3)

Question 10

How to find indices of non-zero elements from [1,2,0,0,4,0]?

Answer 10

nz = np.nonzero([1,2,0,0,4,0])

Question 11

How to create a 3x3 identity matrix?

Answer 11

Z = np.eye(3)

Question 12

How to create a 3x3x3 array with random values?

Answer 12

Z = np.random.random((3,3,3))

Question 13

How to create a 10x10 array with random values and find the minimum and maximum values?

Answer 13

Z = np.random.random((10,10)); Zmin, Zmax = Z.min(), Z.max()

Question 14

How to create a random vector of size 30 and find the mean value?

Answer 14

Z = np.random.random(30); m = Z.mean()

Question 15

How to create a 2D array with 1 on the border and 0 inside?

Answer 15

Z = np.ones((10,10)); Z[1:-1,1:-1] = 0

Question 16

How to add a border (filled with 0’s) around an existing array?

Answer 16

Z = np.pad(Z, pad_width=1, mode='constant', constant_values=0) or use fancy indexing

Question 17

What is the result of 0 * np.nan?

Answer 17

nan

Question 18

What is the result of np.nan == np.nan?

Answer 18

False

Question 19

What is the result of np.inf > np.nan?

Answer 19

False

Question 20

What is the result of np.nan - np.nan?

Answer 20

nan

Question 21

What is the result of np.nan in set([np.nan])?

Answer 21

True

Question 22

What is the result of 0.3 == 3 * 0.1?

Answer 22

False

Question 23

How to create a 5x5 matrix with values 1,2,3,4 just below the diagonal?

Answer 23

Z = np.diag(1+np.arange(4), k=-1)

Question 24

How to create an 8x8 matrix and fill it with a checkerboard pattern?

Answer 24

Z = np.zeros((8,8), dtype=int); Z[1::2,::2] = 1; Z[::2,1::2] = 1

Question 25

How to find the index (x,y,z) of the 100th element in a (6,7,8) shape array?

Answer 25

np.unravel_index(99, (6,7,8))