Grouping dates

[Arthur Boting]

Hello,
I have a file where I have random dates in a year (these are not all the dates of the year). My question is can I group my dates so that they are together for the following 9 days. And then they go a group further for the other 9 days (these would include all the days of the year if this is possible)
Is this possible in stata and if so how?

[Nick Cox]

I can't follow what is needed here, but the function doy() pulls day of the year (1 to 365 or 366) out of daily dates. That would seem to define, when suitably binned, 40 groups of 9 days and 1 group of 5 or 6 days.

[Arthur Boting]

So i have a dataset with a lot of dates (with some dates reoccuring). What i want is having the dates grouped by 9 days so that I can see a movement between the 40 groups

[Nick Cox]

Sorry, but that doesn't take me -- or it seems anyone else -- any further in understanding what you want.