Sum values between two dates in a panel data

[Ellie Yang]

Hello statalist, I have a panel data needs to calculate the sum of a column value between two dates for each studyid. For example, I need sum MsgRepNtwk between the two mark_date and create a new column storing the output. How could I operate it? Thanks very much for helping it out.

[Tom Scott]

Ellie Yang I only know about half of the code to do this, but you're more likely to get help from better people if you supply your data (or a portion of it if the file is large) using dataex instead just posting a picture.

[Nick Cox]

bysort studyid (date) : gen spell = sum(markdate < .) 
bysort studyid spell : egen wanted = total(MsgReptNtwk)

[Ellie Yang]

Thank you all! Next time I will work with dataex!