Re: st: simple calculations across rows

["B. Timothy Walsh" <btw1@columbia.edu>]

Oops! Highly embarrassing--apologies all around. Stata it is!!

Appreciate the quick reply. I believe I can follow your guidance--seems 
straightforward enough.

Thanks very much!
Tim

--On Monday, July 16, 2012 3:58 PM +0100 Nick Cox <njcoxstata@gmail.com> 
wrote:

> Better to say you are a beginning user, as you have not yet learned
> how to spell "Stata"!!!
>
> That detail aside, you can do things like this:
>
> egen mean_1 = mean(measure / (day == 1 & inrange(period, 3, 4))), by(id)
> egen mean_2 = mean(measure / (day == 2 & inrange(period, 3, 4))), by(id)
>
> egen tag = tag(id)
>
> scatter mean_2 mean_1 if tag
>
> On the first device, note that an expression like
>
> (day == 1 & inrange(period, 3, 4))
>
> is 1 when true and 0 when false; correspondingly
>
> measure / expression is measure when expression is 1 and missing (and
> so ignored) when expression is 0. For more, see
>
> Cox, N.J. 2011. Speaking Stata: Compared with ...Stata Journal 11(2):
> 305-314
>
> Note that tagging is necessary to avoid each summary being used 12 times.
>
> Nick
>
> On Mon, Jul 16, 2012 at 3:37 PM, B. Timothy Walsh <btw1@columbia.edu>
> wrote:
>
> > I am a beginner-to-intermediate level STATA user, and would like to find
> > a solution to what I hope is a relatively straightforward problem. I have
> > looked a bit at the archives, and have been led in the direction of mata,
> > but am wondering if another (less daunting?) method might be available.
> >
> > I am importing data from a device and would like to use STATA to do some
> > data reduction. The device monitors types of physical activity over 2
> > days, and the data are provided in rows, each of which contains a
> > summary of data over pre-defined 4 hour blocks, like 8 AM to 12N. So,
> > each subject has 6 rows of data/day and a total of 12 rows for 2 days.
> >
> > What I wish to do is to be able to summarize--like simple averages,
> > etc.--across some but not all time periods, and, maybe, days. For
> > example, for each subject, calculate the total activity over the 8AM to
> > 4PM blocks on day 1 and compare that to the same measure on day 2. Etc.
> >
> > Here is a somewhat simplified outline of how one subject's data might
> > look for the first 3 periods of day 1:
> >
> > ID      DAY             PERIOD  MEASURE
> > i       1               1               Xi11
> > i       1               2               Xi12
> > i       1               3               Xi13
> >
> > I have only a modest dataset, so I do not need particularly efficient
> > code. Better code that is easy to interpret and be modified by a novice
> > such as myself.
> *
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*
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