Levels of a factor
On Jul 24, 2013, at 6:25 AM, Borja Rivier wrote:
Hi all, I am having a bit of trouble using the levels() function. I have a factor with many elements, and when I use the function levels() to extract the list of unique elements, some of the elements returned are not actually in the factor. For example I would have this:
vector <- dataset$Benchmark class(vector)
[1] "factor"
length(vector)
[1] 35615
vector2 <- levels(vector) length(which(!(vector2 %in% vector)))
[1] 235 Does anyone know how this is possible?
When you take a subset of a factor vector, the levels are not reduced to the unique values in the new vector. There is droplevels function that would need to be applied if you already have such a vector, and there is a drop argument that you need to set to TRUE in the `[.factors` call if you want to "attack the problem at the source". ?`[.factor ?droplevels
David Winsemius Alameda, CA, USA