Set value for particular cell in pandas DataFrame using index

In pandas, you can set the value of a specific cell in a DataFrame using the at method. The at method allows you to set the value of a cell by specifying the index of the row and column.

For example, suppose you have a DataFrame called df and you want to set the value of the cell at row index 2 and column 'B' to 5:

import pandas as pd

df = pd.DataFrame({'A': [1, 2, 3], 'B': [4, 5, 6]})

df.at[2, 'B'] = 5

print(df)

Alternatively, you can use the iat method which allows you to set the value of a cell by specifying the index of the row and column using integer based location.

df.iat[2, 1] = 5

You can also use the loc method which allows you to set the value of a cell by specifying the label of the row and column.

df.loc[2, 'B'] = 5

It's worth noting that, these methods are efficient and faster than other common methods like df.ix[], df.iloc[], and df[] when it comes to setting the value of a single cell.

Please keep in mind that, these methods will raise a `KeyError `trigger if the index or column label does not exist.