python - How can I drop non string type 'nan' from list

Question

I have the data coming from the field. It is in list format. The elements are float. Some unexpected character like nan is seen in the list. But it is not in string format. I tried existing solutions but failed to remove them.

My code:

lst = [1.2,2.3,nan]

newlst = [x for x in lst if str(x) != 'nan']

Present output:

NameError: name 'nan' is not defined

Expected output:

newlst = [1.2,2.3]

question from:https://stackoverflow.com/questions/66052031/how-can-i-drop-non-string-type-nan-from-list

Answer 1

There's a math.isnan() which could be used to identify the NaNs. You can use this inside list comprehension to achieve this as:

>>> import math
>>> lst = [1.2,2.3,float('nan')]

>>> [i  for i in lst if not math.isnan(i)]
[1.2, 2.3]

Additionally, one of the property of 'NaN' numbers is that they return False when compared with itself. You can also utilise this property to identify them and filter them out as:

>>> [i  for i in lst if i==i]
[1.2, 2.3]

Refer Why is NaN not equal to NaN? for more details.