Cannot change Numpy array elements filtered by boolean indexing

Question

Reproducible code:

x = np.array([0.9, 0.9, 1])
y = np.array([0, 0, 1])
y[x<1] = 1 - x[x<1]
print(y)

Output

array([0, 0, 1])

Desired output

array([0.1, 0.1, 1])

I know np.where will get me the desired output. I'm just curious about why boolean indexing doesn't work in this case.

Ali_Sh · Accepted Answer · 2022-06-11 11:14:59Z

2

You must specify the dtype for y:

y = np.array([0, 0, 1], dtype=np.float64)

When you did not specify that, it assume integer as dtype. So each modification on this will be converted to original dtype of this array.

answered Jun 11, 2022 at 11:14

Ali_Sh

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