How to exclude a column by name?

This piece of code does the trick. Most important is the which() command:

df = data.frame(a = runif(10), b = runif(10))
df[,-which(names(df) == "a")]

Thanks to you and Linlin.  It did not occur to me to use which(); I thought
that there would be a shorter way to accomplish this since names are
first-class indices for data frames and arrays.  (Or are they?  What happens
under the hood when I write df[,"a"]?)