Pandas Drop Columns with NaN or None Values

pandas.DataFrame.dropna() is used to drop/remove columns with NaN/None values. Python doesn’t support Null hence any missing data is represented as None or NaN values. NaN stands for Not A Number and is one of the common ways to represent the missing values in the data. None/NaN values are one of the major problems in Data Analysis hence before we process either you need to remove columns that have NaN values or replace NaN with empty for String and replace NaN with zero for numeric columns.

Take Away:

• pandas.DataFrame.dropna() is used to drop columns with NaN/None values from DataFrame.
• numpy.nan is Not a Number (NaN), which is of Python build-in numeric type float (floating point).
• None is of NoneType and it is an object in Python.

1. Quick Examples of Drop Columns with NaN Values

If you are in a hurry, below are some quick examples of how to drop columns with nan values in Pandas DataFrame.

# Below are some quick examples

# Drop all columns with NaN values
df2=df.dropna(axis=1)

# Drop columns that has all NaN values
df2=df.dropna(axis=1,how='all')

# With threshold
df2=df.dropna(axis=1,thresh=2)

# Drop columns with NaN Values inplace
df.dropna(axis=1,inplace=True)

Now, let’s create a DataFrame with a few rows and columns and execute some examples to learn using drop columns with nan values. Our DataFrame contains column names Courses, Fee, Duration, and Discount.

import pandas as pd
import numpy as np
technologies = ({
     'Courses':["Spark",'Java',"Hadoop",'Python','PHP'],
     'Fee' :[20000,np.nan,26000,24000,25000],
     'Duration':['30days',np.nan,'35days','40days',np.nan],
     'Discount':[np.nan,np.nan,None,None,np.nan]
               })
df = pd.DataFrame(technologies)
print(df)

Yields below output.

2. Using DataFrame.dropna() to Drop Columns with NaN Values

By using pandas.DataFrame.dropna() method you can drop columns with Nan (Not a Number) or None values from DataFrame. Note that by default it returns the copy of the DataFrame after removing columns. If you want to remove from the existing DataFrame, you should use inplace=True.

# Drop all columns with NaN values
df2=df.dropna(axis=1)
print("After dropping columns with NaN Values:", df2)

Yields below output.

Alternatively, you can also use axis=1 as a param to remove columns with NaN, for example df.dropna(axis=1). Use dropna(axis=0) to drop rows with NaN values from pandas DataFrame.

3. Drop Columns with all NaN values in the DataFrame

Use how param to specify how you want to remove columns. By default how=any which specified to remove columns when NaN/None is present on any element (missing data on any element)

Use how='all' to remove columns that have all NaN/None values (data is missing for all elements in a column)

# Drop columns that has all NaN values
df2=df.dropna(axis=1,how='all')
print(df2)

Yields below output.

# Output:
  Courses      Fee Duration
0   Spark  20000.0   30days
1    Java      NaN      NaN
2  Hadoop  26000.0   35days
3  Python  24000.0   40days
4     PHP  25000.0      NaN

4. Drop Columns with NaN Values inplace of DataFrame

As you have seen, by default dropna() method doesn’t drop columns from the existing DataFrame, instead, it returns a copy of the DataFrame. If you want to drop from the existing DataFrame use inplace=True.

# Drop columns with NaN Values inplace
df.dropna(axis=1,inplace=True)
print("After dropping columns with NaN Values:", df2)

Yields below output.

After dropping columns with NaN Values:  
   Courses
0   Spark
1    Java
2  Hadoop
3  Python
4     PHP

5. Complete Example of Drop Columns with NaN Values

import pandas as pd
import numpy as np
technologies = ({
     'Courses':["Spark",'Java',"Hadoop",'Python','PHP'],
     'Fee' :[20000,np.nan,26000,24000,25000],
     'Duration':['30days',np.nan,'35days','40days',np.nan],
     'Discount':[np.nan,np.nan,None,None,np.nan]
               })
df = pd.DataFrame(technologies)
print(df)

# Drop all columns with NaN values
df2=df.dropna(axis=1)
print(df2)
# Drop columns that has all NaN values
df2=df.dropna(axis=1,how='all')
print(df2)

# Drop columns with NaN Values inplace
df.dropna(axis=1,inplace=True)
print(df)

Conclusion

In this article, you have learned how to drop columns with NaN/None values in pandas DataFrame using DataFrame.dropna(). I also learned how to remove columns only when all values are NaN/None, remove only when selected Columns have NaN values, and remove using in place param.

Happy Learning !!

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• Drop Pandas first column from DataFrame.
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• Pandas Replace Values based on Condition
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• Remove NaN From Pandas Series
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• Count NaN Values in Pandas DataFrame
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• Pandas DataFrame.fillna() function explained
  Pandas Series.fillna() function explained

References

• https://pandas.pydata.org/docs/reference/api/pandas.DataFrame.dropna.html?