NumPy: Exercises and Solutions

Removing extreme values

Exercise

Generate an array of a thousand random numbers
Print out the shape of the array, and the mean and standard deviation of these numbers
Remove all numbers that are more than one standard deviation above or below the mean
Again, print out the shape of the array, and the mean and standard deviation of the remaining numbers

Solution

import numpy as np

a = np.random.random(1000)
m = np.mean(a)
sd = np.std(a)
print('Before removing extreme values:')
print('N = {}, M = {}, SD = {}'.format(len(a), m, sd))
new_a = a[(a > m - sd) & (a < m + sd)]
new_m = np.mean(new_a)
new_sd = np.std(new_a)
print('After removing extreme values:')
print('N = {}, M = {}, SD = {}'.format(len(new_a), new_m, new_sd))

Output:

Before removing extreme values:
N = 1000, M = 0.47584620688058077, SD = 0.2872202276618915
After removing extreme values:
N = 575, M = 0.4660418590730324, SD = 0.16177725026674805

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