On 06/14/04 09:25, jeroen clarysse wrote: >Hi all > >I'm a programmer at the psychology dept, and last week, I was asked to write >an application to analyze some result data from CO2 measurement experiments. >I don't want to reinvent the wheel, so before I start custom coding in C, >I'd though to look around a bit and bumped into R on freshmeat. > >basically, it is a 2-column data sheet, with timings on col1 and CO2 value >on col2. These value have a pretty nice oscillating nature, with some >occasional false spikes. > >the analysis simply means extracting the 'ceilings' of the curves = the >start-end times of the top of each oscilation. > >my Q to the mailinglist is now : can such analysis be done in R ? Or is R >not the appropriate package for this kind of stuff ?
R is certainly the appropriate package - especially for someone with programming experience - but this is not a simple problem no matter what you use. The problem is to eliminate the noise, the "false spikes." I cannot give you the solution, and I notice that nobody else has replied either. But I can tell you that I dealt with a very similar problem (helping the Mozilla Foundation measure the speed of page loading, which turned out to have a periodicity) using various time-series functions, such as acf, as well as trimmed means to get rid of outliers. But the situation was a bit different, as there were several observations at each time point, so I could apply the trimmed mean to that time point. Unfortunately, I don't have time to get more involved in your problem, but this may get you started. I think what you might have to do is iterate between fitting the model and eliminating outliers from the residuals, but maybe some statistician on this list will have a better idea. Jon -- Jonathan Baron, Professor of Psychology, University of Pennsylvania Home page: http://www.sas.upenn.edu/~baron ______________________________________________ [EMAIL PROTECTED] mailing list https://www.stat.math.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html
