Remove NaN From List in Python

Remove
NaN
From the List in Python Using themath.isnan()
Method 
Remove
NaN
From the List in Python Using thenumpy.isnan()
Method 
Remove
NaN
From the List of Strings in Python 
Remove
NaN
From the List in Python Using thepandas.isnull()
Method
This tutorial will look into various methods to find and remove the Nan
values from the list in Python. The NaN
value in programming means Not a Number
, which means the variable’s value is not a number.
If a NaN
value occurs in an array or a list, it can create problems and errors in the calculations. We will also look into ways to remove the string values nan
from the list in this tutorial. We can remove the NaN
or 'nan'
values from the list, by using the following methods.
Remove NaN
From the List in Python Using the math.isnan()
Method
The math.isnan(value)
method takes a number value
as input and returns True
if the value
is a NaN
value and returns False
otherwise. Therefore we can check if there a NaN
value in a list or array of numbers using the math.isnan()
method.
We need the math.isnan()
method because if float('NaN') == float('NaN')
returns False
in Python or we can say that two NaN
values are not equal in Python. The below example code demonstrates how to use the math.isnan()
method to remove the NaN
value from the list.
import math
mylist = [1,2,float('nan'),8,6,4,float('nan')]
print(mylist)
newlist = [x for x in mylist if math.isnan(x) == False]
print(newlist)
Output:
[1, 2, nan, 8, 6, 4, nan]
[1, 2, 8, 6, 4]
Remove NaN
From the List in Python Using the numpy.isnan()
Method
The np.isnan(array)
method, takes the array
as input and returns True
for the corresponding index if it is NaN
value and returns False
otherwise.
The below example code demonstrates how to remove the NaN
values from the list using the numpy.isnan()
method:
import numpy as np
mylist = [1,2,float('nan'),8,6,4,float('nan')]
print(mylist)
newlist = [x for x in mylist if np.isnan(x) == False]
print(newlist)
Output:
[1, 2, nan, 8, 6, 4, nan]
[1, 2, 8, 6, 4]
Remove NaN
From the List of Strings in Python
Now, let’s suppose that the number list is converted to string type, and we want to check if it contains any NaN
values. After converting into the string type, the NaN
value becomes a string equal to 'nan'
and can be easily detected and remove by comparing it with 'nan'
.
The below example code demonstrates how we can remove the NaN
value from the list of string data type:
mylist = [1,2,'nan',8,6,4,'nan']
mylist = [str(x) for x in mylist]
print(mylist)
newlist = [x for x in mylist if x != 'nan']
print(newlist)
Output:
['1', '2', 'nan', '8', '6', '4', 'nan']
['1', '2', '8', '6', '4']
Remove NaN
From the List in Python Using the pandas.isnull()
Method
The pandas.isnull(obj)
takes a scalar or an arraylike obj
as input and returns True
if the value is equal to NaN
, None
, or NaT
; otherwise, it returns False
.
The example code demonstrates how to use the pandas.isnull()
method to remove the NaN
values from Python’s list.
import pandas as pd
mylist = [1,2,float('nan'),8,float('nan'),4,float('nan')]
print(mylist)
newlist = [x for x in mylist if pd.isnull(x) == False]
print(newlist)
Output:
[1, 2, nan, 8, nan, 4, nan]
[1, 2, 8, 4]
Now suppose we do not know the type of the list or if the list contains the data of various data types. In this case, we can check and remove the NaN
values and 'nan'
values from the list using the pandas.isnull()
method by comparing each value of the list with the 'nan'
value.
We can use the pandas.isnull()
method because, unlike the previously mentioned methods, the pandas.isnull()
method does not return an error if the string data type is given as input. Therefore we can use the pandas.isnull()
method to remove the NaN
and 'nan'
value from the list or an array in Python.
The below example code demonstrates how to use the pandas.isnull()
method and the 'nan'
value to remove NaN
and 'nan'
values from the list in Python.
import pandas as pd
mylist = ['John',23,'nan','New York',float('nan')]
print(mylist)
newlist = [x for x in mylist if pd.isnull(x) == False and x != 'nan']
print(newlist)
Output:
['John', 23, 'nan', 'New York', nan]
['John', 23, 'New York']