Sometimes the absence of a name is maked by an NA: x <- 1:2 names(x)[[1]] <- "a" names(x) # [1] "a" NA Whereas other times its y <- c(a = 1, 2) names(y) # [1] "a" "" Is this deliberate? The help for names() is a bit murky, but an example shows the NA behaviour. Hadley -- http://had.co.nz/