change pandas index value base on column condition

I want to change an index value for a specific column condition.

Here an example

import pandas as pd

data = {
    "Product": ["Computer", "Printer", "Monitor"],
    "Price": [120, 25, 40],
}

df = pd.DataFrame(data, index=["Item_1", "Item_1", "Item_1"])

        Product     Price
Item_1  Computer    120
Item_1  Printer     25
Item_1  Monitor     40

I want to modify the index value ‘Item_1’ to ‘TOTO’ for df.loc[df.Product==’Monitor’]
(and without passing by reset_index()).

The result should be:

        Product     Price
Item_1  Computer    120
Item_1  Printer     25
TOTO    Monitor     40

>Solution :

You can use np.where with mask:

df.index = np.where(df.Product == "Monitor", "TOTO", df.index)

print(df)

Prints:

         Product  Price
Item_1  Computer    120
Item_1   Printer     25
TOTO     Monitor     40