Python Pandas - Insert a new index value at the first index from the last

To insert a new index value at the first index from the last, use the index.insert() method. The insert() method takes the position and value as parameters, where position -1 refers to the first index from the last.

Creating a Pandas Index

First, let's create a Pandas index with some sample values ?

import pandas as pd

# Creating the Pandas index
index = pd.Index(['Car', 'Bike', 'Airplane', 'Ship', 'Truck'])

# Display the index
print("Original Pandas Index:")
print(index)

Original Pandas Index:
Index(['Car', 'Bike', 'Airplane', 'Ship', 'Truck'], dtype='object')

Using insert() Method

The insert() method creates a new index with the value inserted at the specified position. Position -1 inserts before the last element ?

import pandas as pd

# Creating the Pandas index
index = pd.Index(['Car', 'Bike', 'Airplane', 'Ship', 'Truck'])

print("Original Index:")
print(index)

# Insert 'Suburban' at position -1 (first index from the last)
new_index = index.insert(-1, 'Suburban')

print("\nAfter inserting 'Suburban' at position -1:")
print(new_index)

Original Index:
Index(['Car', 'Bike', 'Airplane', 'Ship', 'Truck'], dtype='object')

After inserting 'Suburban' at position -1:
Index(['Car', 'Bike', 'Airplane', 'Ship', 'Suburban', 'Truck'], dtype='object')

Understanding Position -1

Position -1 means "before the last element". Here's how different negative positions work ?

import pandas as pd

index = pd.Index(['A', 'B', 'C', 'D'])

print("Original:", index.tolist())
print("Insert at -1:", index.insert(-1, 'X').tolist())
print("Insert at -2:", index.insert(-2, 'Y').tolist())
print("Insert at -3:", index.insert(-3, 'Z').tolist())

Original: ['A', 'B', 'C', 'D']
Insert at -1: ['A', 'B', 'C', 'X', 'D']
Insert at -2: ['A', 'B', 'Y', 'C', 'D']
Insert at -3: ['A', 'Z', 'B', 'C', 'D']

Key Points

• The insert() method returns a new index object; it doesn't modify the original
• Position -1 inserts before the last element
• Negative positions count from the end of the index
• The method maintains the original dtype of the index

Conclusion

Use index.insert(-1, value) to insert a new value at the first position from the last. This creates a new index with the value placed before the final element.