Answering my own question. ?sample (!) y <- by(x, x$TrSeasYr, function(x) mean(sample(x[,1], size=999, replace = TRUE)))
>>> Tim Howard 10/13/2011 9:42 AM >>> All - I have an uneven set of replicates and would like to sample from this set X number of times to generate a mean for each grouping variable. I was thinking the boot package would be the thing to use, but now I'm not so sure ... given the discussion here: http://finzi.psych.upenn.edu/Rhelp10/2010-June/243828.html Given these data (a small subset): > dput(x) structure(list(numSpp = c(7, 8, 6, 4, 5, 4, 10, 12, 7, 13, 4, 11, 4, 3, 3, 10, 8, 16, 11, 6, 3, 5, 6, 13, 15, 2, 6, 11, 11, 10, 6, 9, 11, 14, 10, 7), TrSeasYr = c("1", "1", "1", "1", "1", "1", "1", "1", "1", "1", "1", "1", "1", "1", "1", "2", "2", "2", "2", "2", "3", "3", "3", "3", "3", "3", "3", "3", "3", "3", "3", "3", "3", "3", "3", "3")), .Names = c("numSpp", "TrSeasYr"), row.names = c(NA, -36L), class = "data.frame") #get into R by pasting the above after "x<-" or dget("clipboard") # my grouping var is col 2, data are in col 1 # my attempt using boot library(boot) mn <- function(d,f) { mean(d[,1] * f[d[,1]]) } b1 <- boot(data = x, mn, R=99, stype = "f", strata=x$TrSeasYr) > b1 STRATIFIED BOOTSTRAP Call: boot(data = x, statistic = mn, R = 99, stype = "f", strata = x$TrSeasYr) Bootstrap Statistics : original bias std. error t1* 8.083333 0.1352413 1.681901 > What is the most efficient way to resample, with replacement, and generate means for each grouping variable? Thanks in advance, Tim > sessionInfo() R version 2.12.2 (2011-02-25) Platform: i386-pc-mingw32/i386 (32-bit) locale: [1] LC_COLLATE=English_United States.1252 LC_CTYPE=English_United States.1252 [3] LC_MONETARY=English_United States.1252 LC_NUMERIC=C [5] LC_TIME=English_United States.1252 attached base packages: [1] stats graphics grDevices utils datasets methods base other attached packages: [1] RODBC_1.3-2 boot_1.3-2 loaded via a namespace (and not attached): [1] tools_2.12.2 Timothy G. Howard, Ph.D. Director of Science New York Natural Heritage Program 625 Broadway, 5th floor Albany, NY 12233-4757 (518) 402-8945 facsimile (518) 402-8925 [[alternative HTML version deleted]] ______________________________________________ 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.
