numpy basics

Question 1

import the numpy library

Answer 1

import numpy as np

Question 2

in a 2-D array, what are the axes labels for row and column?

Answer 2

rows - axis 0

cols - axis 1

Question 3

in a 3-D array what are the axes numbered as for rows, columns and array?

Answer 3

rows - axis 0
cols - axis 1
array - axis 2

Question 4

create an array in numpy

Answer 4

a = np.array([2,3,5])

Question 5

create a 2-D array in numpy

Answer 5

two_d = np.array([(3,3,6),(1,4,7)])

Question 6

create a 3-D array in numpy

Answer 6

c = np.array([[(3,4),(1,3)],[(25,2),(1,55)]])

Question 7

create an array of zeroes as integers with a length of 5

Answer 7

x = np.zeros(5, dtype=int)

Question 8

create a 2-d array of zeroes as integers, with dimensions of 5 rows by 3 columns

Answer 8

x = np.zeros((5,3),dtype=int)

Question 9

create an array of even numbers from 2 -> 46 using numpy

Answer 9

a = np.arange(2,47,2)

Question 10

create an array of 10 evenly spaced values between 0 and 64 inclusive

Answer 10

a = np.linspace(0,65,10)

Question 11

create a 3 x 5 matrix (3 rows, 5 columns) filled with the number 10

Answer 11

a = np.full((3,5),10)

Question 12

create an identity matrix measuring 3x3

Answer 12

np.eye(3)

Question 13

create a 2x8 matrix (row x col) filled with random numbers

Answer 13

np.random.random((2,8))

Question 14

see row x col dimensions of an array

Answer 14

a.shape

Question 15

see if 1-d, 2-d, 3-d, etc of an array

Answer 15

a.ndim

Question 16

see data type of an array

Answer 16

a.dtype.name

Question 17

convert array to int

Answer 17

a = a.astype(int)

Question 18

get square root of an array
get log of an array
get exponentiation of array
get sin of an array
get cos of an array

Answer 18

b = np.sqrt(a)
b = np.log(a)
b = np.exp(a)
b = np.sin(a)
b = np.cos(a)

Question 19

get the dot product of transposed matrices

Answer 19

a.dot(b)

Question 20

get sum of an array
get min of an array
get max of rows
get cumulative sum
get mean of array
get median
get standard deviation
copy an array
sort an array

Answer 20

a.sum()
a.min()
a.max(axis=0)
a.cumsum()
a.mean()
a.median()
np.std(a)
b = a.copy()
a.sort()

Question 21

get correlation coefficient between two arrays

Answer 21

np.corrcoef(a,b)

Question 22

transpose and array - what does it mean and how do you do it?

Answer 22

diagonal flip of a matrix…
cols => rows
rows = > cols

b = np.transpose(a)

Question 23

flatten a multi-dimensional array

Answer 23

a.ravel()

Question 24

reshape an array, but don’t change data

Answer 24

a.reshape(2,3)

Question 25

concatenate 2 arrays

Answer 25

c = np.concatenate((a,b), axis=0)

Question 26

stack 2-D array (row-wise)

Answer 26

c = np.vstack(a,b)

Question 27

stack 2-D array (col-wise)

Answer 27

c = np.hstack(a,b)

Question 28

split 2-D array every other row

Answer 28

c = np.vsplit(b, n/2) where n == row length

Question 29

split 2-D array horizontally by every other column

Answer 29

c = np.hsplit(b, n/2) where n == col length