Question

I’m looking for the most efficent way (i.e. the lesser keys pressed) to indexing the last element of an array.

Then something like

a <- c(1,2,3)
n <- length(a)
b <- a[n]

should not be used, I would like to use just a single command.

In the example above I could use

b <- a[length(a)]

but I wonder if something shorter does exist.

Let I want to select a part of an array, like

a <- seq(from = 1, to = 10, by = 1)
b <- a[3:length(a)]

Is there a shorter way to do it?

Answer 1

For the first case, you can use:

> tail(a, 1)
[1] 3

Not that that really qualifies as shorter.

For the second example

> tail(a, -2)
[1]  3  4  5  6  7  8  9 10

but in general; no there is nothing shorter. R doesn’t have an inplace operator or syntactic sugar for the end of a vector or array, in the sense of something that evaluates to the end of the array. That is what length() can be used for.