python - Replacing minimum element in a numpy array subject to a condition -

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i need replace element of numpy array subject minimum of numpy array verifying 1 condition. see following minimal example:

arr = np.array([0, 1, 2, 3, 4]) label = np.array([0, 0, 1, 1, 2]) cond = (label == 1) label[cond][np.argmin(arr[cond])] = 3

i expecting label now

 array([0,  0,  3,  1, 2])

instead getting

 array([0,  0,  1,  1, 2])

this consequence of known fact numpy arrays not updated double slicing.

anyway, can't figure out how rewrite above code in simple way. hint?

you triggering numpy's advanced indexing chaining of indexing, assigning doesn't go through. solve this, 1 way store indices corresponding mask , use indexing. here's implementation -

idx = np.where(cond)[0] label[idx[arr[idx].argmin()]] = 3

sample run -

in [51]: arr = np.array([5, 4, 5, 8, 9])     ...: label = np.array([0, 0, 1, 1, 2])     ...: cond = (label == 1)     ...:   in [52]: idx = np.where(cond)[0]     ...: label[idx[arr[idx].argmin()]] = 3     ...:   in [53]: idx out[53]: array([2, 3])  in [54]: label out[54]: array([0, 0, 3, 1, 2])

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