Numpy where using a list of values

Question

if I wanted to create a filter for a numpy array for several values how would I write that.

For instance say I want to do this...

clusters = np.array([4, 570, 56, 2, 5, 1, 1, 570, 32, 1])
fiveseventy_idx = np.where((clusters == 1) | (clusters == 570 ))
clusters = clusters[ fiveseventy_idx ]

In the above case i just want 2 items but say I had a much larger array and I want to filter for n number of items, I don't see how this could be done using this syntax if I had say 300 items I wanted out of the original array.

It can't really be done efficiently. You might be better with a for item in clusters: / if item in my_desired_set: construct. — Tim Roberts
– Tim Roberts, Commented Feb 28, 2022 at 4:11

aaossa · Accepted Answer · 2022-02-28 04:32:56Z

3

If you had a sequence of values to search in your clusters, you could use np.isin:

>>> targets = [1, 570]  # Also could be: np.array([1, 570])
>>> np.isin(clusters, targets)
array([False,  True, False, False, False,  True,  True,  True, False,                       True]) 
>>> clusters[np.isin(clusters, targets)]
array([570,   1,   1, 570,   1])

answered Feb 28, 2022 at 4:32

aaossa

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