Saullo Castro Saullo Castro - 9 months ago 41
Python Question

NumPy array, change the values that are NOT in a list of indices

I have a

numpy
array like:

a = np.arange(30)


I know that I can replace the values located at positions
indices=[2,3,4]
using for instance fancy indexing:

a[indices] = 999


But how to replace the values at the positions that are not in
indices
? Would be something like below?

a[ not in indices ] = 888


Thank you!

Answer Source

I don't know of a clean way to do something like this:

mask = np.ones(a.shape,dtype=bool) #np.ones_like(a,dtype=bool)
mask[indices] = False
a[~mask] = 999
a[mask] = 888

Of course, if you prefer to use the numpy data-type, you could use dtype=np.bool_ -- There won't be any difference in the output. it's just a matter of preference really.