numPy

Question 1

how to import numpy in python?

Answer 1

import numpy as np

we usually assign the package to a variable named np

Question 2

how to create a numpy array (numpy.ndarray) with 3 elements, all zeros? (assign to a variable named “a”)

Answer 2

a = np.zeros(3)

Question 3

how to create a numpy array (numpy.ndarray) with 6 elements, all ones? (assign to a variable named “a”)

Answer 3

a = np.ones(6)

Question 4

how to create a 2 dimensional numpy array (numpy.ndarray) with shape 6, 4 with elements all zeros? (assign to a variable named “a”)

Answer 4

a = np.zeros((6,4))

the parameter is a tuple!

Question 5

how to print the variable named “v” in Jupyter to see its content?

Answer 5

v

Question 6

how to print the first element of one dimensional numpy array “a” in Jupyter to see its content?

Answer 6

a[0]

Question 7

how to print the type of variable “v” in Jupyter?

Answer 7

type(v)

Question 8

how to print the shape of a numpy array named “a” in Jupyter?

Answer 8

a.shape

this is the numpy.ndarray.shape function

Question 9

how to change the shape of a numpy array named “a” in Jupyter to (4,5)?

Answer 9

a.shape = (4,5)

with a tuple

Question 10

how to create a one dimensional numpy array, starting with 10, ending with 30, with equally distant elements, 12 of them altogether?
(assign to variable “a”)

Answer 10

a = np.linspace(10,30,12)

Question 11

create a python list of 4,5,8 and immidiately convert to a numpy array and assign to a variable named “a”

Answer 11

a = np.array([4,5,8])

Question 12

how to efficiently access the last element in a python list named l?

Answer 12

l[-1]

Question 13

“a” array or list has 10 elements. Access the elements indexed 3,4,5

Answer 13

a[3:6]

Question 14

create an array with 50 random floats, evenly distributed, from
0 to 10

Answer 14

a = np.random.rand(50)*10

Question 15

create an array with 20 random integers from 0 to 10 (including 10 as a possible value)

Answer 15

a = np.random.randint(0,11,size=20)

Question 16

access every second element of a list or array, starting from the first

Answer 16

a[::2]

Question 17

how to return an array of booleans, indicating if numpy array “a” values are greater than 5 or not at corresponding indexes?

Answer 17

a > 5

Question 18

use numpy to return mean of array “a”

Answer 18

np.mean(a)

Question 19

use numpy to return standard deviation of array “a”

Answer 19

np.std(a)

Question 20

use numpy to return sum of array “a”

Answer 20

np.sum(a)

Question 21

use numpy to return variance of array “a”

Answer 21

np.var(a)

Question 22

use numpy to return minimum of array “a” and also the index of the first occurance of it

Answer 22

minOfA = np.min(a)
firstIndexOfMinOfA = np.argmin(a)

Question 23

use numpy to return an array which contains the elements of array “a” that are greater than 3

Answer 23

a[a > 3]

Question 24

change array “a” so that the values greater than 10 will be 5, the other will be 0

Answer 24

a = np.where(a > 10, 5, 0)

Question 25

“a” and “b” are both numpy arrays with same length. Create a numpy array “c” which has also same length and the elements are the sums of corrwsponding elements of “a” and “b” arrays

Answer 25

c = a + b

Question 26

add 5 to all elements of “a” numpy array

Answer 26

a = a + 5

Question 27

dot product of two numpy arrays “a” and “b”

Answer 27

a @ b

Question 28

sort array “a”

Answer 28

np.sort(a)

Question 29

use numpy to create an array with 1000 elements that are standard normally distributed

Answer 29

a = np.random.normal(0,1,1000)

Question 30

calculate histogram parameters of array “a”

Answer 30

np.histogram(a)

Question 31

get the current working directory

Answer 31

import os

d = os.getcwd()

Question 32

create an array “a” with a sequence evenly spaced, each value is followed with itself+0.2, starting with 3, ending with 6

Answer 32

a = np.arange(3,6,0.2)