Pandas: Add and Insert New Elements into a Series

This succinct article is about adding and inserting new elements to an existing Series in Pandas.

Before we begin, allow me to clarify an important point: “add elements” implies appending new elements to the end of the Series, while “insert elements” implies inserting new elements at a specific position in the Series.

Adding Elements to a Series

In the old days, the append() method was also a popular approach for this task, but is now depreciated so I won’t mention it anymore (it still works but you will see some annoying warnings when running your code).

Instead, for new Pandas projects, you should use the pd.concat() function to append a single value, a list of values, or another Series object to a given Series. This will return a new Series object with the combined elements.

Example:

import pandas as pd

s1 = pd.Series([10, 20, 30])

# append a single value
s1 = pd.concat([s1, pd.Series([40])])

# append a list of values
s1 = pd.concat([s1, pd.Series([50, 60, 70])])

# append another series
s2 = pd.Series([80, 90, 100])
s1 = pd.concat([s1, s2])

print(s1) 

Output:

0     10
1     20
2     30
0     40
0     50
1     60
2     70
0     80
1     90
2    100
dtype: int64

Inserting an Element into a Series at a Specific Position

In scenarios where you want to insert an element at a specific position in a Series, you can use the loc indexer with a fractional index and then sort and reset the indices.

Example

Suppose we have a Series called fruits containing the following elements: apple, banana, and orange. Here’s how we can insert a new element pear after the second element banana in the Series:

import pandas as pd

fruits = pd.Series(["apple", "banana", "orange"])

# insert new element with a fractional index
fruits[1.5] = "pear"

# sort and reset index
fruits = fruits.sort_index().reset_index(drop=True) 

print(fruits)

Output:

0     apple
1    banana
2      pear
3    orange
dtype: object

If you don’t sort and reset the indices, the newly inserted element won’t be at your desired position. This step is important but often overlooked.