remove the last element of a vector

Question

I need to remove the last number in a groups of vectors, i.e.:

v <- 1:3 v1 <- 4:8 

should become:

v <- 1:2 v1 <- 4:7 

Answer 1

You can use negative offsets in head (or tail), so head(x, -1) removes the last element:

R> head( 1:4, -1) [1] 1 2 3 R>  

This also saves an additional call to length().

Edit: As pointed out by Jason, this approach is actually not faster. Can't argue with empirics. On my machine:

R> x <- rnorm(1000) R> microbenchmark( y <- head(x, -1), y <- x[-length(x)], times=10000) Unit: microseconds                 expr    min      lq median     uq     max 1   y <- head(x, -1) 29.412 31.0385 31.713 32.578 872.168 2 y <- x[-length(x)] 14.703 15.1150 15.565 15.955 706.880 R>  

Answer 2

Use length to get the length of the object and - to remove the last one.

v[-length(v)] 

A negative index in R extracts everything but the given indices.