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st: Testing for a contiguous subset of observations?

From   BW Wheeler <>
Subject   st: Testing for a contiguous subset of observations?
Date   Fri, 30 Nov 2007 11:18:49 -0000

Dear all,

I'm having trouble figuring out a solution to this data management problem, and have exhausted all books and findit (partly as it's hard to know what to search for)!

I have time series data captured from accelerometers, with an observation of 'activity counts' logged every 10 seconds for several days for each individual. If the number of counts is zero continuously for any period of 10 minutes or more (i.e. 60+ observations), we need to assume that the accelerometer was not being worn, and to treat these zeros as missing.

So, my data look something like this:

Observation Date Time Activity
1 13/05/2006 15:20:00 230
2 13/05/2006 15:20:10 215
3 13/05/2006 15:20:20 0
4 13/05/2006 15:20:30 0
5 13/05/2006 15:20:40 0

Does anyone have any ideas of how I can replace the 'Activity' value with missing, if that value is a zero in the midst of a continuous series of 60+ zeros?

Any advice very gratefully received

Ben Wheeler
Research Fellow
Department of Social Medicine, University of Bristol
& South West Public Health Observatory

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