Summing values conditionally

I have a list of values that was imported from a text file. It's the volume of a stock that’s traded for each minute the market is open. I'd like to track the running sum of the value throughout the day (i.e. @ 9:31 it's trades 100 shares for the day, at 9:32 its traded another 65 shares making the total 165 shares so far today, etc..).

Is there a way to conditionally sum the values based on the date field? The import of the historical data is all connected so that when I try to sum the values the running total continues day to day. I've tried to put a row in between each day's data; however the file has several years worth of data and it's at least a full day project.

Any guidance is greatly appreciated.

Thank You
Derek

Do you have a column with both date and time or a separate date and time column? If it's the former in column A and amounts to total in B you could use this formula in c1 copied down

=IF(INT(A1)=INT(A2),"",SUMPRODUCT(--(INT(A$1:A1)=INT(A1)),B$1:B1))

gives a total on the last entry for each day

Maybe you can edit this formula to your needs.