Numpy: find index of the elements within range

I have a numpy array of numbers, for example,

a = np.array([1, 3, 5, 6, 9, 10, 14, 15, 56])  

I would like to find all the indexes of the elements within a specific range. For instance, if the range is (6, 10), the answer should be (3, 4, 5). Is there a built-in function to do this?

Solution 1:

You can use np.where to get indices and np.logical_and to set two conditions:

import numpy as np
a = np.array([1, 3, 5, 6, 9, 10, 14, 15, 56])

np.where(np.logical_and(a>=6, a<=10))
# returns (array([3, 4, 5]),)

Solution 2:

As in @deinonychusaur's reply, but even more compact:

In [7]: np.where((a >= 6) & (a <=10))
Out[7]: (array([3, 4, 5]),)

Solution 3:

I thought I would add this because the a in the example you gave is sorted:

import numpy as np
a = [1, 3, 5, 6, 9, 10, 14, 15, 56] 
start = np.searchsorted(a, 6, 'left')
end = np.searchsorted(a, 10, 'right')
rng = np.arange(start, end)
rng
# array([3, 4, 5])