numpy

Question 1

How do you use numpy as a shortcut?

Answer 1

• import numpy as np

Question 2

Given an array my_list([1,2,3]), create an array ‘arr’ that is composed of my_list.

Answer 2

1. my_list = [1,2,3]
2. arr = np.arry(my_list)
3. arr

Question 3

Practice Creating ndarrays:

1. How do you create a 1-dimensional numpy array of a list of three values?
2. How do you create a 2-dimensional numpy array of two, three value lists?

Answer 3

1. x = np.array([1,2,3])
2. m = np.array([1,2,3], [4,5,6])

Question 4

Create an array of even numbers from 0 to 10

Answer 4

np.arange(0,11,2)

Question 5

How do you print the number of rows and columns in an array?

Answer 5

• m = np.array([1,2,3],[4,5,6])
• print(m.shape)
  
  • returns (2,3
  • ‘2’ is the number of rows, ‘3’ is the number of columns

Question 6

Create an array composed of values between 0 and 14

Answer 6

np.arange(15)

Question 7

How do you create a 1-dimensional array of even values between 0 and 30?

How would you reshape this array into a 3 x 5 array?

Answer 7

• n = np.arange(0, 30, 2)
• the np.arange syntax is (x, y, z), where:
  
  • x = min range value (inclusive)
  • y = max range value (exclusive)
  • z = step value
• To reshape this array:
  
  • n = n.reshape(3, 5)

Question 8

How do you create an array of 9 evenly spaced values from range 0 to 4?

How do you change the size of the array to a 3 x 3 array?

Answer 8

• o = np.linspace(0, 4, 9)
• o.resize(3,3)

Question 9

How do you create a 3 x 2 array of 1’s?

Answer 9

• np.ones((3,2))

Question 10

How do you create a 2 by 3 array of 0’s?

Answer 10

• np.zeros((2, 3))

Question 11

How do you create a 3 x 3 array with 1’s in the diaganol?

Answer 11

• np.eye(3)

Question 12

Given an array y = np.array([4,5,6]), how would you create a 3 x 3 array with the ‘y-array’ through the diagnol?

Answer 12

• np.diag(y)

Question 13

Given an array p = np.ones([2,3]), how would you create a vertical stack of the array ‘p’ and an additional array of each integer within the p-array multiplied by 2?

Answer 13

• np.vstack([p, 2*p])

Question 14

Given an array p = np.ones([2,3]), how would you create a horizontal stack of the array ‘p’ and an additional array of each integer within the p-array multiplied by 2?

Answer 14

• np.hstack([p, 2*p])

Question 15

Given an array a = np.array([-4, -2, 1, 3, 5]),

1. how would you add all of the values of the array together?
2. how would you find the max value of the array?
3. how would you find the min value of the array?
4. how would you find the mean of the array?
5. how would you find the standard deviation of the array?
6. how would you find the max index value of the array?
7. how would you find the min index value of the array?

Answer 15

1. a.sum()
2. a.max()
3. a.min()
4. a.mean()
5. a.std()
6. a.argmax()
7. a. argmin()

Question 16

Given the array s = np.arange(13)**2, how would you find?

1. the first value of the array
2. the fifth value of the array
3. the range of the first three values of the array

Answer 16

1. s[0]
2. s[4]
3. s[0:3]

Question 17

1. For an array ‘z’, how would you transpose the rows and columns?
2. For an array ‘z’, how would you see what type of data the array has?
3. For an array ‘z’, how would yo cast the array to the type ‘float’?

Answer 17

1. z.T
2. z.dtype
3. z.astype(‘f’)

Question 18

• What is an important distinction about Python’s built in lists when it comes to slicing arrays?

Answer 18

• Array slices are views on the original array.
• This means that the data is not copied, and any modifications to the view will be reflected in the source array.

Question 19

For a 6 x 6, 2-dimensional array ‘r’, how would you get:

1. the value three rows in and three columns downn?
2. he values in the third row from the fourth column over?
3. the first two rows, including all columns except the last column?
4. every other value of the last row?
5. set every value to ‘0’?

Answer 19

1. r[2,2]
2. r[3, 3:6]
3. r[:2, :-1]
4. r[-1, ::2]
5. r[:] = 0

Question 20

For a given array ‘r’, how can you copy the array?

Answer 20

• r_copy = r.copy()

Question 21

How do you create a 4 x 3 array of random integers between the range of 0 and 9?

Answer 21

• test = np.random.randint(0, 10, (4, 3))

Question 22

Python is an example of an ________ language?

Answer 22

interpreted

Question 23

What is the result of the following code: [‘a’, ‘b’, ‘c’] + [1, 2, 3]?

Answer 23

[‘a’, ‘b’, ‘c’, 1, 2, 3]