R: removing the last elements of a vector
RVectorElementsR Problem Overview
How can I remove the last 100 elements of a zoo series?
I know the name[-element] notation but I can't get it work to substract a full section
R Solutions
Solution 1 - R
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 - R
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 - R
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
Solution 4 - R
Just use the numeric indices, ie
N <- nrow(X)
X <- X[1:(N-100-1),]
where you should need to ensure N is larger 100 etc
Solution 5 - R
if you're a one liner
x = x[1:(length(x) -101)]
Solution 6 - R
Another one-liner for the sake of completeness:
x <- lag(x, 100)[-1:-100]