Here are two ways. The second way is more than 10x faster. > set.seed(1) > C <- sample(c("a", "b"), 100000, replace = TRUE) > system.time(s1 <- ifelse(C == "a", 1, -1)) user system elapsed 0.37 0.01 0.38 > system.time(s2 <- 2 * (C == "a") - 1) user system elapsed 0.02 0.00 0.02 > identical(s1, s2) [1] TRUE
On 7/4/07, Keith Alan Chamberlain <[EMAIL PROTECTED]> wrote: > Dear Rhelpers, > > Is there a faster way than below to set a vector based on values from > another vector? I'd like to call a pre-existing function for this, but one > which can also handle an arbitrarily large number of categories. Any ideas? > > Cat=c('a','a','a','b','b','b','a','a','b') # Categorical variable > C1=vector(length=length(Cat)) # New vector for numeric values > > # Cycle through each column and set C1 to corresponding value of Cat. > for(i in 1:length(C1)){ > if(Cat[i]=='a') C1[i]=-1 else C1[i]=1 > } > > C1 > [1] -1 -1 -1 1 1 1 -1 -1 1 > Cat > [1] "a" "a" "a" "b" "b" "b" "a" "a" "b" > > Sincerely, > KeithC. > Psych Undergrad, CU Boulder (US) > RE McNair Scholar > > ______________________________________________ > 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. > ______________________________________________ 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.