st: Testing for a contiguous subset of observations?

[BW Wheeler <ben.wheeler@bristol.ac.uk>]

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
Thanks,
Ben

----------------------
Ben Wheeler
Research Fellow
Department of Social Medicine, University of Bristol
& South West Public Health Observatory
ben.wheeler@bristol.ac.uk

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