Pandas dropna() – Drop Null/NA Values from DataFrame

1. Pandas DataFrame dropna() Function

Pandas DataFrame dropna() function is used to remove rows and columns with Null/NaN values. By default, this function returns a new DataFrame and the source DataFrame remains unchanged.

We can create null values using None, pandas.NaT, and numpy.nan variables.

The dropna() function syntax is:

dropna(self, axis=0, how="any", thresh=None, subset=None, inplace=False)

• axis: possible values are {0 or ‘index’, 1 or ‘columns’}, default 0. If 0, drop rows with null values. If 1, drop columns with missing values.
• how: possible values are {‘any’, ‘all’}, default ‘any’. If ‘any’, drop the row/column if any of the values is null. If ‘all’, drop the row/column if all the values are missing.
• thresh: an int value to specify the threshold for the drop operation.
• subset: specifies the rows/columns to look for null values.
• inplace: a boolean value. If True, the source DataFrame is changed and None is returned.

Let’s look at some examples of using dropna() function.

2. Pandas Drop All Rows with any Null/NaN/NaT Values

This is the default behavior of dropna() function.

import pandas as pd
import numpy as np

d1 = {'Name': ['Pankaj', 'Meghna', 'David', 'Lisa'], 'ID': [1, 2, 3, 4], 'Salary': [100, 200, np.nan, pd.NaT],
      'Role': ['CEO', None, pd.NaT, pd.NaT]}

df = pd.DataFrame(d1)

print(df)

# drop all rows with any NaN and NaT values
df1 = df.dropna()
print(df1)

Output:

     Name  ID Salary Role
0  Pankaj   1    100  CEO
1  Meghna   2    200  None
2   David   3    NaN  NaT
3    Lisa   4    NaT  NaT

     Name  ID Salary Role
0  Pankaj   1    100  CEO

3. Drop All Columns with Any Missing Value

We can pass axis=1 to drop columns with the missing values.

df1 = df.dropna(axis=1)
print(df1)

Output:

     Name  ID
0  Pankaj   1
1  Meghna   2
2   David   3
3    Lisa   4

4. Drop Row/Column Only if All the Values are Null

import pandas as pd
import numpy as np

d1 = {'Name': ['Pankaj', 'Meghna', 'David', pd.NaT], 'ID': [1, 2, 3, pd.NaT], 'Salary': [100, 200, np.nan, pd.NaT],
      'Role': [np.nan, np.nan, pd.NaT, pd.NaT]}

df = pd.DataFrame(d1)

print(df)

df1 = df.dropna(how='all')
print(df1)

df1 = df.dropna(how='all', axis=1)
print(df1)

Output:

     Name   ID Salary Role
0  Pankaj    1    100  NaT
1  Meghna    2    200  NaT
2   David    3    NaN  NaT
3     NaT  NaT    NaT  NaT

     Name ID Salary Role
0  Pankaj  1    100  NaT
1  Meghna  2    200  NaT
2   David  3    NaN  NaT

     Name   ID Salary
0  Pankaj    1    100
1  Meghna    2    200
2   David    3    NaN
3     NaT  NaT    NaT

5. DataFrame Drop Rows/Columns when the threshold of null values is crossed

import pandas as pd
import numpy as np

d1 = {'Name': ['Pankaj', 'Meghna', 'David', pd.NaT], 'ID': [1, 2, pd.NaT, pd.NaT], 'Salary': [100, 200, np.nan, pd.NaT],
      'Role': [np.nan, np.nan, pd.NaT, pd.NaT]}

df = pd.DataFrame(d1)

print(df)

df1 = df.dropna(thresh=2)
print(df1)

Output:

     Name   ID Salary Role
0  Pankaj    1    100  NaT
1  Meghna    2    200  NaT
2   David  NaT    NaN  NaT
3     NaT  NaT    NaT  NaT

     Name ID Salary Role
0  Pankaj  1    100  NaT
1  Meghna  2    200  NaT

The rows with 2 or more null values are dropped.

6. Define Labels to look for null values

import pandas as pd
import numpy as np

d1 = {'Name': ['Pankaj', 'Meghna', 'David', 'Lisa'], 'ID': [1, 2, 3, pd.NaT], 'Salary': [100, 200, np.nan, pd.NaT],
      'Role': ['CEO', np.nan, pd.NaT, pd.NaT]}

df = pd.DataFrame(d1)

print(df)

df1 = df.dropna(subset=['ID'])
print(df1)

Output:

     Name   ID Salary Role
0  Pankaj    1    100  CEO
1  Meghna    2    200  NaN
2   David    3    NaN  NaT
3    Lisa  NaT    NaT  NaT

     Name ID Salary Role
0  Pankaj  1    100  CEO
1  Meghna  2    200  NaN
2   David  3    NaN  NaT

We can specify the index values in the subset when dropping columns from the DataFrame.

df1 = df.dropna(subset=[1, 2], axis=1)
print(df1)

Output:

     Name   ID
0  Pankaj    1
1  Meghna    2
2   David    3
3    Lisa  NaT

The ‘ID’ column is not dropped because the missing value is looked only in index 1 and 2.

7. Dropping Rows with NA inplace

We can pass inplace=True to change the source DataFrame itself. It’s useful when the DataFrame size is huge and we want to save some memory.

import pandas as pd

d1 = {'Name': ['Pankaj', 'Meghna'], 'ID': [1, 2], 'Salary': [100, pd.NaT]}

df = pd.DataFrame(d1)

print(df)

df.dropna(inplace=True)
print(df)

Output:

     Name  ID  Salary
0  Pankaj   1   100.0
1  Meghna   2     NaN

     Name  ID  Salary
0  Pankaj   1   100.0

8. References

• Python Pandas Module Tutorial
• Pandas Drop Duplicate Rows
• Pandas DataFrame dropna() API Doc