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From |
Nick Cox <njcoxstata@gmail.com> |

To |
statalist@hsphsun2.harvard.edu |

Subject |
Re: st: simple calculations across rows |

Date |
Mon, 16 Jul 2012 15:58:33 +0100 |

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. * * For searches and help try: * http://www.stata.com/help.cgi?search * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/

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