NumPy - Aggregation Functions
What is the output of the following code?
import numpy as np arr = np.array([2, 4, 4, 4, 5, 5, 7, 9]) print(np.var(arr))
What is the output of the following code?
medium📝 Predict Output Q13 of 15
Step-by-Step Solution
Solution:
Step 1: Calculate the mean of the array
The array is [2,4,4,4,5,5,7,9]. Sum = 40, count = 8, mean = 40/8 = 5.Step 2: Calculate variance
Variance = average of squared differences from mean:
(2-5)^2=9, (4-5)^2=1, (4-5)^2=1, (4-5)^2=1, (5-5)^2=0, (5-5)^2=0, (7-5)^2=4, (9-5)^2=16
Sum = 9+1+1+1+0+0+4+16 = 32
Variance = 32/8 = 4.0Step 3: Check code output
NumPy'snp.var()by default calculates population variance (divides by N). So output is 4.0.Final Answer:
4.0 -> Option BQuick Check:
Variance = 4.0 [OK]
Quick Trick: Variance = mean of squared differences [OK]
Common Mistakes:
- Calculating sample variance (dividing by N-1) instead of population
- Mixing variance with standard deviation
- Incorrect mean calculation
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