如何在numpy数组中为标量变量赋值？

Question

I wrote a for-loop and wished to assign the value to the first variable in the part of an array that equals to -inf . The complete code is as below:

cList = np.full((5), -np.inf)
for i in range(5):
    newest = another_array[i][1]
    cList[cList==-np.inf][0] = newest

The code didn't throw any errors. However the value assignment was failed. Do you have any idea about it? Thanks in advance!

Answer 1

This:

cList[cList==-np.inf]

makes a copy of the selected data, not a view, so this:

cList[cList==-np.inf][0] = newest

modifies the copy, leaving cList unchanged.

Repeatedly searching cList for instances of -inf is a really inefficient way to go about this. The best solution will depend on the details of your program. For the simple example you've posted, you could just do

c = another_array[:5, 1].copy()  # or just another_array[:5, 1] if a view is fine

For more complex cases, you might want to create an array of values to assign and do

c[c == -np.inf] = values