通过分组将缺失值替换为多个列的先前值

I have a dataframe of 6 variables. For each column, data is same for the same group with some missing values. I want to fill these missing values by duplicating value of the same group for each variable. In case all values are missing for a particular group, it should fill value of above group. So, I want the result as df_complete.I have a dataframe of 6 variables. For each col