On Wed, 2009-08-26 at 08:06 -0700, Phil Spector wrote: > The ave function is very handy for things like this: > > mins = ave(D$Var,D$Site,FUN=function(x)min(x[x>0],na.rm=TRUE)) > D$Var = ifelse(is.na(D$Var) | D$Var == 0,mins,D$Var) > > should do the required replacements.
Thanks Phil, that's great. I hadn't come across ave() before. Shortly after I received your email, it dawned on me to just rep the minimums the required number of times (by the number of non-missing 0's) for each site, and then insert this vector into the data frame whilst subsetting on whether it was zero or not. Cheers, G > > - Phil Spector > Statistical Computing Facility > Department of Statistics > UC Berkeley > spec...@stat.berkeley.edu > > > On Wed, 26 Aug 2009, Gavin Simpson wrote: > > > Dear List, > > > > I'm wondering if there is a better/cleaner/more efficient way of > > replacing 0 values in a variable with the minimum of the non-missing and > > non-zero values of that same variable, but doing it within the levels of > > a factor? > > > > Consider the dummy example data presented at the end of my message. > > Within each 'Site' there are some 0 values and possibly some NA's. I can > > compute the minimum of the non-missing and non-zero values by 'Site' as > > indicated below using aggregate for example. Save for looping over the > > 'Site's and replacing 0's with the relevant minimum is there a way of > > using a vectorised approach to do the replacement? > > > > Thanks in advance, > > > > G > > > > ## dummy data > > set.seed(123) > > D <- data.frame(Site = factor(rep(LETTERS[1:5], times = 10)), > > Var = runif(5*10)) > > D <- D[with(D, order(Site, Var)), ] > > ## simulate some 0's > > D[c(1,3,11,12,23,27,34,36,41,49), "Var"] <- 0 > > ## just to complicate matters, some NA > > D[sample(NROW(D), 3), "Var"] <- NA > > head(D) > > ## Compute minimums per Site > > aggregate(D$Var, by = list(Site = D$Site), > > FUN = function(x) min(x[x>0], na.rm = TRUE)) > > ## How replace the appropriate 0's with the appropriate minimum? > > -- > > %~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~% > > Dr. Gavin Simpson [t] +44 (0)20 7679 0522 > > ECRC, UCL Geography, [f] +44 (0)20 7679 0565 > > Pearson Building, [e] gavin.simpsonATNOSPAMucl.ac.uk > > Gower Street, London [w] http://www.ucl.ac.uk/~ucfagls/ > > UK. WC1E 6BT. [w] http://www.freshwaters.org.uk > > %~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~% > > > > ______________________________________________ > > R-help@r-project.org 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. > > -- %~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~% Dr. Gavin Simpson [t] +44 (0)20 7679 0522 ECRC, UCL Geography, [f] +44 (0)20 7679 0565 Pearson Building, [e] gavin.simpsonATNOSPAMucl.ac.uk Gower Street, London [w] http://www.ucl.ac.uk/~ucfagls/ UK. WC1E 6BT. [w] http://www.freshwaters.org.uk %~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~% ______________________________________________ R-help@r-project.org 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.
