I’ve got a dataframe that looks a bit like this although there’s more columns.

    Client ID   Fulfilled date
0   309032  2017-05-04
1   309032  2017-06-29
3   331793  2017-07-19
5   319659  2017-05-11
6   321682  2017-05-16

I want to create a flag column is_first_time for first time visitor.

Thought the logic was simple:

def first_time_visitor(self):
    # Create a copy of 'self.df' and sort it by 'Client ID' and 'Fulfilled date'
    temp_df = self.df.copy()
    temp_df.reset_index(inplace=True) #thought this would create a column called index that I could use later.
    temp_df.sort_values(['Client ID', 'Fulfilled date'], inplace=True)
    # Create a new column in 'temp_df' that marks the first occurrence of each client_id
    temp_df['is_first_time'] = ~temp_df['Client ID'].duplicated(keep='first')

    # Convert the boolean values to integers
    temp_df['is_first_time'] = temp_df['is_first_time'].astype(int)
    temp_df = temp_df.sort_values("index")

I then thought I could do something like:

self.df['is_first_time'] = temp_df['is_first_time']

But I get a key error

KeyError: 'index'