Hi my dataframe look like: Store,Dept,Date,Sales 1,1,2010-02-05,245 1,1,2010-02-12,449 1,1,2010-02-19,455 1,1,2010-02-26,154 1,1,2010-03-05,29 1,1,2010-03-12,239 1,1,2010-03-19,264 Simply, I need to add another column called '_id' as concatenation of Store, Dept, Date like "1_1_2010-02-05", I assume I can do it through df['id'] = df['Store'] +'' +df['Dept'] +'_'+df['Date'], but it turned out to be not. Similarly, i also need to add a new column as log of sales, I tried df['logSales'] = math.log(df['Sales']), again, it did not work.