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Re: st: Adding up prior iterations of a variable in a time series dataset


From   Benedikt Achatz <benedikt.achatz@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: Adding up prior iterations of a variable in a time series dataset
Date   Sun, 24 Jun 2012 17:30:46 +0200

Thank you Nick, it worked like a charm.

Am 24.06.2012 17:27, schrieb Nick Cox:
Cumulative sums are usually best calculated with the -sum()- function.

What you want may be more like

bysort page_id (time_var) : gen clicks_to_date = sum(clicks)

Nick

On Sun, Jun 24, 2012 at 3:41 PM, Benedikt Achatz
<benedikt.achatz@gmail.com> wrote:

I am a student and rather new to Stata, and i just can't figure out how this
works. I have been browsing the web for some time and haven't found a
solution that worked for me.

I have a dataset that contains observations of websites at different points
in time. There is a variable, clicks, that contains the clicks in one time
period. What I need to do now is to create a variable clicks_to_date that
contains the clicks in every time period before the current one, including
that one.

This is the code I have been using thus far, without much success...

   levelsof page_id, local(pg_id)
   levelsof time_var, local(tm_vr)

   cap drop clicks_to_date
   gen clicks_to_date = 0

   local clicks_old = 0
   foreach id in `pg_id'{
        foreach x in `tm_vr'{
        if `x' == 1 {local clicks_old = 0
        }
        replace clicks_to_date = clicks+`clicks_old'
        display `clicks_old'
        local clicks_old = clicks_to_date
        }
   }

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