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How does the pandas series.first_valid_index() method work?
The pandas series.first_valid_index() method is used to get the index of the first valid data. This means the first_valid_index() method returns the index of the first 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 first_valid_index() method doesn’t take any parameter.
Example 1
Let’s take a series object and try to retrieve the first valid index.
# importing packages
import pandas as pd
import numpy as np
# create a series
s = pd.Series([None, np.nan, 27, 61,np.nan, 34, 52, np.nan, 17], index=list('abcdefghi'))
print(s)
# apply first_valid_index() method
result = s.first_valid_index()
print("Result:")
print(result)Explanation
Initially, we have created a pandas series object by using the pandas.Series constructor with a list of Nan’s and integer values and the index of the series is specified by an index parameter with a list of strings.
Output
The output is as follows −
a NaN b NaN c 27.0 d 61.0 e NaN f 34.0 g 52.0 h NaN i 17.0 dtype: float64 Result: c
For the above example, the first valid index is “c”, because the elements at index positions a, b are Null/NA values.
Example 2
Here, let’s take an empty series object and see how the first_valid_index() method works for an empty series.
# importing packages
import pandas as pd
# create a series
sr = pd.Series([])
print(sr)
# apply first_valid_index() method
result = sr.first_valid_index()
print("Result:")
print(result)Output
The output is given below −
Series([], dtype: float64) Result: None
The first_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 first_valid_index() method to get the 1st valid index.
# importing packages
import pandas as pd
import numpy as np
# create a series
sr = pd.Series([None, np.nan])
print(sr)
# apply first_valid_index() method
result = sr.first_valid_index()
print("Result:")
print(result)Output
The output is given below −
0 NaN 1 NaN dtype: float64 Result: None
For this example, also the first_valid_index() method returned None because there is no valid element available in the given series object.
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