How to index ndarray in tuple using boolean with Numpy Python?

Question

I would like to index ndarray in a tuple using a boolean mask such as below

import numpy as np
n_max = 5
list_no = np.arange ( 0, n_max )
lateral = np.tril_indices ( n_max, -1 )
mask= np.diff ( lateral [0].astype ( int ) )
mask [-1] = 1
Expected=lateral[mask!= 0]

However, when executing the line Expected=lateral[mask!= 0], the compiler return an error

TypeError: only integer scalar arrays can be converted to a scalar index

Expected=
0 = {ndarray: (4,)} [1 2 3 4]
1 = {ndarray: (4,)} [0 1 2 3]

May I know where did I do wrong?

@hpaulj, I have edited the thread, but to answer your question the error occur at the last line lateral[mask!-0] — rpb
– rpb, Commented Jan 20, 2021 at 5:53
Tell us about lateral. You could even show the whole thing! Be generkus with the information. Good answers show results. — hpaulj
– hpaulj, Commented Jan 20, 2021 at 5:55
It is a 2D coordinate. and I would like to extract certain 2D coordinate if it fulfill the boolean condition. I hope this answer this your question @hpaulj — rpb
– rpb, Commented Jan 20, 2021 at 5:57
No. From the docs I see it is a tuple. We index a tuple with a simple number. a boolean array works on arrays, not tuples. — hpaulj
– hpaulj, Commented Jan 20, 2021 at 6:36

SJ11 · Accepted Answer · 2021-01-20 11:12:09Z

1

So it seems like the size of the mask and lateral[0] are different. Since mask is the difference between each element in the array, it is of size n-1 when lateral[0] is of size n. You might want to append to the mask array instead. Also, since lateral is a tuple, you would need to index on the tuple before applying the mask.

You might be need something like this:

import numpy as np
n_max = 5
list_no = np.arange(0, n_max)
lateral = np.tril_indices(n_max, -1)
mask = np.diff(lateral[0].astype(int))
mask = np.append(mask, 1)
expected_0 = lateral[0][mask != 0]
print(expected_0)
expected_1 = lateral[1][mask != 0]
print(expected_1)

answered Jan 20, 2021 at 11:12

SJ11

2541 silver badge3 bronze badges

Sign up to request clarification or add additional context in comments.

Collectives™ on Stack Overflow

How to index ndarray in tuple using boolean with Numpy Python?

1 Answer 1

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Your Answer

Sign up or log in

Post as a guest

Related