Masking and Filtering Arrays with NumPy
Array masking allows you to select elements based on conditions or boolean arrays.
Example: Boolean Masking
import numpy as np
a = np.array([True, True, True, False, False])
b = np.array([[1, 2, 3, 4, 5],
[1, 2, 3, 4, 5]])
filtered = b[:, a]
print(filtered)
# Output:
# [[1 2 3]
# [1 2 3]]
Example: Masking with Conditions
x = np.array([1, 2, 3, 4, 5])
mask = x > 2
print(x[mask]) # Output: [3 4 5]
Tips
- The mask must be a boolean array of the same length as the dimension being indexed.
- You can combine conditions using
&(and),|(or), and~(not), e.g.,(x > 2) & (x < 5).