I am pretty pleased with baselines I fit to chromatograms using the runquantile() function in caTools(v1.6) when its probs parameter is set to 0.2 and its k parameter to ~1/20th of n (e.g., k ~ 225 for n ~ 4500, where n is time series length). This ignores occasional low- side outliers, and, after baseline subtraction, I can re-adjust any negative values to zero. But runquantile's computation time proves exceedingly long for my large datasets, particularly if I set the endrule parameter to 'func'. Here is what caTools author Jarek Tuszynski says about relative speeds of various running-window functions:
- runmin, runmax, runmean run at O(n) - runmean(..., alg="exact") can have worst case speed of O(n^2) for some small data vectors, but average case is still close to O(n). - runquantile and runmad run at O(n*k) - runmed - related R function runs at O(n*log(k)) The obvious alternative runmin() performs poorly due to dropout (zero- and low-value 'reverse-spikes') in the data. And runmed fits a baseline that, upon subtraction, obviously will send half the values into the negative, not suitable for my application. I jimmied something together with runmin and runmedian that is considerably faster; unfortunately, the fit seems less good, at least by eye, due still to the bad runmin behavior. I'd be interested in other baseline fitting suggestions implemented or implementable in R (I'm using v. 2.4.1pat under WinXP). Why, for instance, can I not find a running trimmean function? Because it offers no computational savings over runquantile? Also, the 'func' setting for the caTools endrule parameter--which adjusts the value of k as ends are approached--is said not to be optimized (using this option does add further time to computations). Is there an alter- native that would be speedier, e.g., setting endrule = "keep" and then subsequently treating ends with R's smoothEnds() function? -John Thaden Little Rock, Arkansas USA Confidentiality Notice: This e-mail message, including any a...{{dropped}} ______________________________________________ R-help@stat.math.ethz.ch mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.