r - Collapse consecutive runs of numbers to a string of ranges

Question

Let's say I have the following vector of numbers:

vec = c(1, 2, 3, 5, 7, 8, 9, 10, 11, 12)

I'm looking for a function that will create a string summarizing the list of numbers the way a human would. That is, each run of consecutive numbers (here 1, 2, 3 and 7, 8, 9, 10, 11, 12) is collapsed into its start and end value:

"1-3, 5, 7-12"

How can I do this in R?

Answer 1

Adding another alternative, you could use a deparseing approach. For example:

deparse(c(1L, 2L, 3L))
#[1] "1:3"

Taking advantage of as.character "deparse"ing a given "list" as input, we could use:

as.character(split(as.integer(vec), cumsum(c(TRUE, diff(vec) != 1))))
#[1] "1:3"  "5"    "7:12"
toString(gsub(":", "-", .Last.value))
#[1] "1-3, 5, 7-12"