There is a lot of detail that you are expecting members to upload here. I have not tried, but I have some broad strategic advice, exactly as before.
There is no _obvious_ need here for subdividing into smaller datasets followed by recombination.
What is most evident is that you have a subdivision into time periods. So, create a variable that is 1, 2, etc. for your distinct time periods and then use that new variable -by:- as in previous problems.
One of the easy details about -by:- is that you can define blocks of observations on as many criteria as you wish.
Nick
[email protected]
Hua Pan
Now I have a big problem and have thought about it over and over again and can’t find the way to solve it. Maybe someone here has can help me.
I have two datasets, say A and B. A has permno (identify nr.), daily return and date. B has permno, repdate (report date).
A
permno date ret
10001 01.Apr.2004 .01793105
10001 02.Apr.2004 -.046070479
10001 05.Apr.2004 .022727251
10001 06.Apr.2004 -.005555551
10001 07.Apr.2004 .016759828
… … …
10001 31.Dec.2008 …
10002 01.Apr.2004 .018296152
10002 02.Apr.2004 .010668194
… … …
10002 31.Dec.2008 …
10003 01.Apr.2004 …
… … …
93105 … …
B:
Permno repdate
10001 21.Apr.2004
10001 20.July.2004
10001 26.Oct.2004
10001 03.Feb.2005
04.May.2005
… …
10002 23.Apr.2004
10002 22.July.2004
… …
93105 …
…
I wish to calculate cumulative daily return for each company and for each period, from the next two days after the report day to the day before next report day e.g. for permno 10001, I want to calculate the cumulative return for periods: (21.Apr.2004 +2= 23.Apr.2004, 20.July.2004 -1=19.Juli.2004), (22.July.2004, 25.Oct.2004), (28.Oct.2004, 02.Feb.2005)……for permno 10002, from 23.Apr.2004+2+1=26.Apr.2004 (because 25.Apr.2004 is Sunday, so I have to plus one day), to 21.July.2004……
(cumulative return for each day within period are to be calculated, almost 60 for each period)
At first I tried to get dataset A and B together with merge, but not successful.
use "C:\A.dta", clear
sort permno date
save "C:\A.dta", replace
use "C:\B.dta", clear
sort permno repdate
merge permno using "C:\A.dta"
keep if _merge == 3
drop _merge
save "C:\AB.dta”
Many of date and returns of A are deleted. Maybe I should try joinby, or just change A as Master Data? How can I put them orderly together?
Then I wish that I can build several groups according to the permno and report date:
group1: permno 10001 with daily return from 23.Apr.2004 to 19.Juli.2004
group2: permno 10001 with daily return from 22.July.2004 to 25.Oct.2004
group3: permno 10001 with daily return from 28.Oct.2004 to 02.Feb.2005
….
group n: permno 10002 with daily return from 26.Apr.2004 to 21.July.2004
…..
group m: permno 93105 with…..
After I drop the Observations that don’t belong to any group, I can calculate cumulative return for each group, (thank Austin again for this code)
bys group: g cumul=1+ret if _n==1
replace cumul=(1+ret)*l.cumul if mi(cumul)
replace cumul=cumul-1
Finally I drop the group with missing value and calculate the mean cumulative return for those that have the same group number
by group, sort: generate nr=_n
by nr, sort: egen mean_cumul=mean(cumul)
So the question is how can I put two dataset together and then put the observations into groups according to permno and report date and pay attention that the period begins and ends with work day. When I solve this problem, then I can calculate the mean cumulative return.
Any suggestion would be greatly appreciated. Thank you very much.
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