R: removing the last elements of a vector

Solution 1:

I like using head for this because it's easier to type. The other methods probably execute faster though... but I'm lazy and my computer is not. ;-)

x <- head(x,-100)
> head(1:102,-100)
[1] 1 2

Solution 2:

Actually, there's a much faster way:

y <- x[1:(length(x)-1)]

Code show:

> microbenchmark( y <- head(x, -1), y <- x[-length(x)],y <- x[1:(length(x)-1)], times=10000)
 Unit: microseconds
                      expr    min      lq     mean  median      uq      max
          y <- head(x, -1) 71.399 76.4090 85.97572 78.9230 84.2775 2795.076
        y <- x[-length(x)] 53.623 55.5585 65.15008 56.5680 61.1585 2523.141
 y <- x[1:(length(x) - 1)] 25.722 28.2925 36.43029 29.1855 30.4010 2410.975

Solution 3:

I bet length<- is the most efficient way to trim a vector:

> x <- 1:10^5
> length(x)
[1] 100000
> length(x) <- 3
> x
[1] 1 2 3