Need to sort NaN in Python to the end of a list-CodePudding

I'm trying to sort a list and work around Python's poor handling of nan and inf.

I need to partition a list into all the numbers sorted (or reversed) and at the end of the list any NaN or Inf. The order of the non-number (NaN/Inf) elements is not important, so long as they are arranged at the end of the list.

For example:

n = [13, 4, 52, 3.1, float('nan'), float('inf'), 8.2]
print(n)
o = sorted(n, key = lambda x : float('inf') if (x != x) else x)
print(o)
print(reversed(o))

The o works, and outputs:

[3.1, 4, 8.2, 13, 52, nan, inf]

But using reversed outputs:

[inf, nan, 52, 13, 8.2, 4, 3.1]

Which is not what I want.

I want it to reverse only the values that aren't nan and inf.

Desired output:

[52, 13, 8.2, 4, 3.1, nan, inf]

CodePudding user response：

Use sorted with math.isinf and math.isnan to detect whether it the value either is nan or inf. If they are real numerical values, I negate them for reversing their order.

Example:

import math
n = [13, 4, 52, 3.1, float('nan'), float('inf'), 8.2]
lst = sorted(n, key=lambda x: (math.isinf(x) or math.isnan(x), -x))
print(lst)

Output:

[52, 13, 8.2, 4, 3.1, nan, inf]

If you don't want to reverse the values:

print(sorted(n))

Is enough.

Output:

[3.1, 4, 8.2, 13, 52, nan, inf]