python - Pandas: Trouble Updating Rows Conditionally -
i have following dataframe: >>>df rtt requests asn 1000 4000 100 2000 50 nan 3000 18000 300 my goal divide rtt requests in place if requests not nan , otherwise leave rtt untouched. i've tried various things , either second row gets set nan so: >>>df rtt requests asn 1000 40 100 2000 nan nan 3000 60 300 or dataframe isn't updated @ all desired final output >>>df rtt requests asn 1000 40 100 2000 50 nan 3000 60 300 use fillna in [1889]: df['rtt'] = df['rtt'].div(df['requests']).fillna(df['rtt']) in [1890]: df out[1890]: rtt requests asn 1000 40.0 100.0 2000 50.0 nan 3000 60.0 300.0 or, / instead of div in [1895]: (df['rtt'] / df['requests']).fillna(df['rtt']) out[1895]: asn 1000 40.0 2000 50.0 3000 60.0 dtype: float64 or, combine_first in [1897]: df['rtt'].div(df[...