coding variable values into classes using R

The cut method as outlined by @Greg is probably what you want here. One thing to note is that cut returns a factor by default, which you can suppress by supplying labels = FALSE to return the integer values:

cut(data$wt, c(178, 200, 300, Inf), labels = FALSE)

Alternatively, if your cutting does not lend itself to natural breaks, you can use ifelse(). You can "nest" the ifelse statements similar to Excel. I use "with" to cut down on the typing needed:

data$group2 <- with(data, ifelse(wt >= 179 & wt < 200, 1,   ifelse(wt >= 200 & wt < 300, 2, 3)))

You can try cut

anim <- c(1,2,3,4,5,6,7,8,9,10,11,12,13,14,15) wt <-c(181,179,180.5,201,201.5,245,246.4,189.3,301,354,369,205,199,394,231.3) data <- data.frame(anim,wt)

EDIT: fixed group - right = FALSE, got rid of split example.

group = cut(data$wt, c(178, 200, 300, Inf), right=FALSE)data$swt = as.numeric(group)data   anim    wt swt1     1 181.0   12     2 179.0   13     3 180.5   14     4 201.0   25     5 201.5   26     6 245.0   27     7 246.4   28     8 189.3   19     9 301.0   310   10 354.0   311   11 369.0   312   12 205.0   213   13 199.0   114   14 394.0   315   15 231.3   2> 

I think Greg's answers cover "standard operating procedure", but I find many uses for the findInterval function as well. It naturally returns a number that identifies the interval in the second argument.

 data$int <- findInterval(data$wt, c(179, 200, 300, Inf)) data