Build a new array from an existing using a boolean mask

Question

I have created a boolean mask, say mask, which I want to apply to an existing array, say old to create an entirely new one, say new, which retains only the non zero elements. The new array should then have a smaller dimension with respect to old.

Can some one suggest me the fastest and more coincise way, without using, if possible, the numpy.append function?

Please create an MCVE with inputs, and desired output

Nils Werner
– Nils Werner

2018-12-04 11:56:54 +00:00
Commented Dec 4, 2018 at 11:56 — Nils Werner
– Nils Werner, Commented Dec 4, 2018 at 11:56

yatu · Accepted Answer · 2018-12-04 11:57:32Z

1

Say you have:

old = np.array([2,4,3,5,6])
mask = [True, False, True, False, False]

Simply do:

new = old[mask]
print(new)
[2 3]

I suggest you read about Boolean or “mask” index arrays

answered Dec 4, 2018 at 11:57

yatu

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blue note · Accepted Answer · 2018-12-04 11:56:42Z

0

Just use logical indexing

x = x[x!=0]

answered Dec 4, 2018 at 11:56

blue note

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