R：间隔中的点均等，但不包括端点

Question

Suppose I want to generate equally spaced points within an interval in R, I found the seq function will do this, but the results shows as:

seq(0, 1, length.out = 10)
[1] 0.0000000 0.1111111 0.2222222 0.3333333 0.4444444 0.5555556 0.6666667
[8] 0.7777778 0.8888889 1.0000000

If we want to generate 0.1, 0.2,...,0.9, 1.0 , how could I include one end point and not the other one?

Thanks!

Answer 1

Another option similar to @duckmayr's answer with an additional aligned argument

fun <- function(minimum, maximum, length_out, aligned = c("left", "right")) {
  type <- match.arg(aligned)
  step <- maximum / length_out

  if(type == "left") {
    seq(minimum, right - step, length.out = length_out)
  } else {
    seq(minimum + step, right, length.out = length_out)
  }
}

fun(0, 1, 10) # default is "left"
# [1] 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

fun(0, 1, 10, "right")
# [1] 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

fun(0, 1, 10, "abc")

error in match.arg(aligned) : 'arg' should be one of “left”, “right”

Answer 2

You could do that programatically with something like this:

f <- function(from, to, length.out) {
    length.out <- length.out + 1
    result <- seq(from, to, length.out = length.out)
    result <- result[-1]
    return(result)
}

f(0, 1, 10)
# [1] 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

The idea is that we'll make a sequence with length one more than what you actually want; this will space the elements how you want them, then we just discard the unwanted initial element.