Printing indices corresponding to a criterion in Python-CodePudding

I have an array T. I am printing all values which meet the criterion: T<5. However, I don't know how to print the corresponding indices of values meeting this criterion. I present the expected output.

import numpy as np
T=np.array([4.7,5.1,2.9])
T1=T[T<5]
print([T1])

The expected output is

J=[0,2]

CodePudding user response：

Try np.flatnonzero: np.flatnonzero(T<5)

CodePudding user response：

argwhere does that for you https://numpy.org/doc/stable/reference/generated/numpy.argwhere.html

x = np.arange(6).reshape(2,3)

array([[0, 1, 2],
       [3, 4, 5]])

np.argwhere(x>1)
array([[0, 2],
       [1, 0],
       [1, 1],
       [1, 2]])

The meaning of output is:

row 0 element 2
row 1 element 0
row 1 element 1
row 1 element 2