Getting max value from a list with None elements

Question

I'm trying to get maximal value from a list object that contains nonetype using the following code:

import numpy as np

LIST = [1,2,3,4,5,None]
np.nanmax(LIST)

But I received this error message

'>=' not supported between instances of 'int' and 'NoneType'

Clearly np.nanmax() doesn't work with None. What's the alternative way to get max value from list objects that contain None values?

Answer 1

First, convert to a numpy array. Specify dtype=np.floatX, and all those Nones will be casted to np.nan type.

import numpy as np

lst = [1, 2, 3, 4, 5, None]

x = np.array(lst, dtype=np.float64)
print(x)
array([  1.,   2.,   3.,   4.,   5.,  nan])

Now, call np.nanmax:

print(np.nanmax(x))
5.0

To return the max as an integer, you can use .astype:

print(np.nanmax(x).astype(int)) # or int(np.nanmax(x))
5

This approach works as of v1.13.1.