NumPy where - How to get the subarray of a NumPy array satisfying a condition

To get the subarray of an array satisfying the condition, numpy.where can be used like sql where.

import numpy

a = numpy.array([3, 5, 7, 9, 11])

b = numpy.where(a > 5)

print(b)  # (array([2, 3, 4]),)
print(type(b))  # <class 'tuple'>

where returns a tuple and the first element is a NumPy array. It is an array of the original indexes satisfying the condition a > 5. So b is, to be exact, not a subarray of a.

import numpy

a = numpy.array([3, 5, 7, 9, 11])

b = numpy.where(a > 5)
c = a[b]

print(b)  # (array([2, 3, 4]),)
print(c)  # [ 7  9 11]

The above code shows how to get the subset satisfying a > 5. b is an array of indexes so a[b] is the subarray of a satisfying a > 5.

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