Pandas Dataframe row selection combined condition index- and column values

Question

I want to select rows from a dataframe based on values in the index combined with values in a specific column:

df = pd.DataFrame([[0, 2, 3], [0, 4, 1], [0, 20, 30], [40, 20, 30]], 
                  index=[4, 5, 6, 7], columns=['A', 'B', 'C'])


    A   B   C
4   0   2   3
5   0   4   1
6   0  20  30
7  40  20  30

with

df.loc[df['A'] == 0, 'C'] = 99

i can select all rows with column A = 0 and replace the value in column C with 99, but how can i select all rows with column A = 0 and the index < 6 (i want to combine selection on the index with selection on the column)?

Answer 1

You can use multiple conditions in your loc statement:

df.loc[(df.index < 6) & (df.A == 0), 'C'] = 99