Replacement of matlab find function in python

Question

I am trying to find suitable python function to replace matlab find in my script and with some google search I see np.where() solves the purpose most of the time. But in case of double condition, I have different outputs. Can someone tell me whats wrong with this approach and how to go ahead? The example code and difference is below.

In case of matlab:

b = [1, 2, 3; 1, 2, 3; 1, 2, 3]
[I, J] = find(( b > 1) & (b <= 3))

Gives output

I =                 J = 
     1                 2
     2                 2
     3                 2
     1                 3
     2                 3
     3                 3

In case of python:

b= array([[1, 2, 3],
       [1, 2, 3],
       [1, 2, 3]])

>>> np.where((b > 1) & (b <= 3))
(array([0, 0, 1, 1, 2, 2]), array([1, 2, 1, 2, 1, 2]))

Acorbe · Accepted Answer · 2014-03-06 11:12:36Z

4

Both methods do provide the same answer, although order and indexing conditions are different.

Python indexing of arrays starts from 0, like in C, whilst matlab's one starts from 1.

Moreover, the two outputs (by matlab and numpy) do correspond one another modulo a permutation of the terms. Likely this is due to different indexing implementations.

You can see that matlab goes through your matrix by columns, while numpy by rows.

edited Mar 6, 2014 at 11:12

answered Mar 5, 2014 at 15:29

Acorbe

8,4115 gold badges43 silver badges68 bronze badges

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

1 Comment

Ashish Over a year ago

Thanks. If I transpose the matrix to perform the operation in Python I get the same answer as by Matlab. Just that it returns J as I now and I as J, but that is OK.

Collectives™ on Stack Overflow

Replacement of matlab find function in python

1 Answer 1

1 Comment

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

1 Comment

Your Answer

Sign up or log in

Post as a guest

Linked

Related