filtering arrays

[dramauh]

Hi everyone,

This is my first post in this forum. This question is not related with homework but it is really basic question. So I hope this is the correct section. The other day I was filtering some data using this similar routine

A=X
A[A==0]=numpy.nan

I did this to prevent the modification of the ndarray X. The interesting part is my array X was also modified!! I am not sure why. Thank you so much in advance for your help

Kind regards,

Estanislao

PD: I used python 3.7

[Yoriz]

A==0 resolves to True or False, True & False are also represented as 0 & 1

A[A==0]=numpy.nan

will change value at the index of 0 or 1 depending on the outcome of A==0

Edit: may have gone off in a tangent

A=X

A is now pointing to the same object that X is
you would need a copy of x, presuming x is a list

A=X[:]

[dramauh]

Hi Yoriz,

Yes, I know how it works that command. I used it a lot in MATLAB. My question is why that command modified the array A and the array X. I would have expected that only the array A is modified.

Regards,

[Yoriz]

See the additional edit about copying in the above post
numpy.copy

[dramauh]

Hi Yoriz,

Thank you so much. That was extremely helpful. I did not know the existence of that function.

Regards,