Python Part 4: Numpy

Question 1

axis = 0 in a 2d array

vertical or horizontal?

Answer 1

vertical

Question 2

axis = 1

vertical or horizontal for 2d array?

Answer 2

horizontal

Question 3

create an array with the numbers 1, 2, 3, 4, 5

Answer 3

arr = np.array([1,2,3,4,5])

arr = np.arange(1,6)

Question 4

create an array of 10 zeros

create an array of ones with the dimensions 3x4

Answer 4

arr1 = np.zeros(10)
arr2 = np.ones((3,4))

Question 5

create an array with a range of numbers

• create an array with 0,1,2
• create an array with 3,4,5

Answer 5

np.arange(range)

zB
arr1=np.arange(3)
arr2=np.arange(3,6)

Answer 6

np.random.randint(): 4 occurrences

Question 7

numpy.random.rand():

Answer 7

Create an array of the given shape and populate it with random samples from a uniform distribution over [0, 1).

Answer 8

np.mean(): 4 occurrences

Question 9

Standard Deviation?

Answer 9

np.std(array)

also

np.std(array, axis = x)

Question 10

Variance ?

Answer 10

np.var(array)

Question 11

Array Reshaping ?

Answer 11

arr.reshape(new dimensions)

arr = np.arange(12)
newarr = arr.reshape(4,3)
print(newarr)

Question 12

arr = np.arange(12)
newarr = arr.reshape(4,3)
print(newarr)

output?

Answer 12

[[ 0 1 2]
[ 3 4 5]
[ 6 7 8]
[ 9 10 11]]

Question 13

arr1=np.arange(3)
arr2=np.arange(3,6)

output arrays?

Answer 13

[0 1 2]
[3 4 5]

Question 14

numpy.random.randn():

Answer 14

Generate random numbers from a standard normal distribution

Question 15

numpy.random.randint():

Answer 15

Generate random integers between specified limits.

Question 16

numpy.random.shuffle():

Answer 16

Shuffle the elements of an array randomly.

Question 17

initialise an 1x5 array of random integers smaller than 16

Answer 17

xarr1=np.random.randint(16,size=5)

Question 18

initialise a 3x3 array of random integers >= 7 and < 12

Answer 18

xarr2=np.random.randint(7,12,size=(3,3))

Question 19

Initialise a 3x5 array, choosing numbers randomly from the set (3, 5, 7, 9)

Answer 19

x = random.choice([3, 5, 7, 9], size=(3, 5))