Retrieve Last Valid Index from Pandas Series

The pandas series.last_valid_index() method is used to get the index of the last valid element from the given series object. This means the last_valid_index() method returns the index of the last non_null element of the series.

It will return a single scalar based on the type of series index, and it will return None if the given series has all null/NA values or if it is empty. The method doesn’t have any parameters.

Example 1

Let’s create a pandas series object and retrieve the last valid index by using the last_valid_index() method.

# importing packages
import pandas as pd
import numpy as np

# create a series
s = pd.Series([None, 34, np.nan, 87], index=list('pqrs'))
print(s)

# apply last_valid_index() method
result = s.last_valid_index()

print("Result:")
print(result)

Output

The output is as follows −

p    NaN
q    34.0
r    NaN
s    87.0
dtype: float64

Result:
s

For the above example, the last valid index is “s”, because the element at index position s is not a Null/NA value.

Example 2

Here, let’s take an empty series object and see how the last_valid_index() method works for an empty series.

# importing packages
import pandas as pd

# create an empty series
sr = pd.Series([])
print(sr)

# apply last_valid_index() method
result = sr.last_valid_index()

print("Result:")
print(result)

Output

The output is mentioned below −

Series([], dtype: float64)

Result:
None

The last_valid_index() method returned None for the empty series object.

Example 3

In this following example, we have created a pandas series object with all Null/Nan values and applied the last_valid_index() method to get the last valid index.

# importing packages
import pandas as pd
import numpy as np

# create a series
sr = pd.Series([None, np.nan])
print(sr)

# apply last_valid_index() method
result = sr.last_valid_index()

print("Result:")
print(result)

Output

The output is given below −

0    NaN
1    NaN
dtype: float64

Result:
None

For this example, the last_valid_index() method returned None, because there is no valid element available in the given series object.