how to get a percentage corresponding to groups on my report?

Hi All,

I have a group on my report by USER_ID and then by Activity_Name and I am displaying the detailed data for LOG_DATE, LOG_VALUE, STD_TIME and PRODUCTIVE_HOURS as seen below:

USER_ID                    LOG_DATE          LOG_VALUE          STD_TIME          PRODUCTIVE_HOURS

abcdef                        

Chart Maintenance     

                                   08/15/2016               10                         2.5                         7.5

                                   08/16/2016               20                         3.5                         7.5

Check In/Out              

                                   08/15/2016               20                         3.5                         7.5

                                   08/16/2016               25                         4                            7.5

I need to create a formula on this report that will calculate the Productivity of the Employee by doing a Sum of STD_TIME for a particular LOG_DATE and divide by the PRODUCTIVE_HOURS for that date.

As an example, for the USER abcdef, his/her productivity for 08/15/2016 is equal to ((2.5+3.5)/7.5) * 100 = 80% and for the LOG_DATE of 08/16/2016, the users Productivity is ((3.5+4)/7.5)*100 = 100%

I have created this formula (Sum ({@StdPerHour_num}, {USERS.USER_NAME},GroupName ({PRODUCTIVITY_LOG.LOG_DATE}, "daily"))/{@Max_Prod_Hours}) * 100

but this gives an error stating "A Group condition must be a string" by highlighting the GroupName ({PRODUCTIVITY_LOG.LOG_DATE}, "daily" field in the formula.

Any advise on how to create this formula to achieve the desired result is much appreciated.

Thanks,

Nimish