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# Re: st: calculating cumulative values of other observations

 From KOTa To statalist@hsphsun2.harvard.edu Subject Re: st: calculating cumulative values of other observations Date Sat, 7 Apr 2012 17:12:23 -0400

```thanks Eric,
i did adapt your code for real dataset without problems (see my
previous response)

i am just interested how to do it using Nick's code, which works much
faster (dataset is pretty large).
i am probably missing some thing about how "sum" works or about
boundary conditions

my rewrite of Nick was:

bysort ID activity (date_start): gen priorhrs = sum(hours) - hours if
(date_start>=date_end[_n-1] & !mi(date_end[_n-1]))

which does not work :/

regards
K.

El día 7 de abril de 2012 14:09, Eric Booth <eric.a.booth@gmail.com> escribió:
> <>
>
> On Apr 7, 2012, at 9:42 AM, KOTa wrote:
>
>> thanks Erik, Nick
>>
>> both ways work on this sample, and i managed to adjust for a real database also.
>>
>> few followup question:
>>
>> 1. Eric, any specific reason why you convert time into date format? I
>> used it without conversion and it looks fine.
>> Also on real data your solution somehow goes into infinite loop after
>> finishing all calculations.
>>
> I don't know how you edited the code, so I don't know how you produced an infinite loop?  It certainly doesn't do that with the example I gave you.  Also, I created a time/date format version of "date" just out of habit, I find that it makes data management easier.  If you don't need/want it, then skip it.
>
>
>> 2. Nick, the solution you proposed with "sum" was the one i tried
>> initially. The problem is that in real data I have 2 columns for date
>> (start_date end_date) and i want to compare start_date [_n] >=
>> end_date[all previous]
>> Eric's solution works longer, but i could adjust it to work with
>> different date columns.
>> your solution is works much faster in case there is one date column,
>> but i could not figure out how to do the same with 2 different
>> columns.
>
> El día 7 de abril de 2012 04:08, Nick Cox <njcoxstata@gmail.com> escribió:
>> Why not
>> bysort id activity (time): gen priorhrs = sum(time) - time
>> Nick
>
>
> Nick's -sum- solution does work (and is more straightforward than my -replace line)  with a slight tweak - changing the first "time" to "date2" (if you create the time/date var from my example).  Also, if you are using the same variable names from your original example you'd change "time" to "hours".  Adding this to my example works:
>
>  bysort ID activity (date2): gen njc = sum(hours) - hours
>
>
> Adapting mine and Nick's code to your "real" dataset is another issue completely - if you cannot figure how to adapt our tips to your data/code, then you should post a data & code example/question that is closer to reality.
>
>
> - Eric
> __
> Eric A. Booth
> Public Policy Research Institute
> Texas A&M University
> ebooth@ppri.tamu.edu
> Office: +979.845.6754
>
>
>
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```