用 np.nan 替换列表中的所有值

Question

How to replace all values within a list with np.nan?

a = [1.58, 2.13, 3.98, 4.12]

and what i want is

a = [nan, nan, nan, nan]

I have tried many options like replace or list comprehension, but it didn't work.

Answer 1

A numpy way of doing it natively:

a = np.full(shape=4, fill_value=np.nan).tolist()

Scales well to higher dimensions and larger size.

Answer 2

import numpy as np
a = [1,2,3,4]
a = [np.nan]*len(a)
print(a)

Output:

[nan, nan, nan, nan]

Answer 3

import numpy as np
a = np.full_like(a, np.nan).tolist()

Answer 4

If you want to update the existing list a then you can do this:

a[:] = [np.nan] * len(a)

or even more efficiently - using a generator, rather than constructing a new list just for the assignment:

a[:] = (np.nan for v in a)

But if you don't mind throwing a away and replacing it with a whole new list, then you can just do:

a = [np.nan] * len(a)