[R] how to get a numeric vector?

[Martin Maechler]

>>>>> Avi Gross via R-help 
>>>>>     on Sun, 4 Oct 2020 19:50:43 -0400 writes:

    > Always hard to tell if THIS is a homework project. As with
    > most things in R, if you can not find at least a dozen
    > ways to do it, it is not worth doing.

    > The question (way below) was how to take two vectors of
    > length two and make a longer results based on using the
    > ":" operator to generate a range between the first element
    > of each array and then between the second elements and
    > return the combined results as a vector.

    > Using simple loops on the length of the two vectors you
    > want combined this way can be done either in-line or by
    > making a simple function.

    > Something like this:

    > results = c()

    > for (index in 1:length(a)) {
    >   results <- c(results, a[index]:b[index])
    > }

    > The above generalizes to any size vectors of the same length.

    > There are probably lots of ways to do this using functional programming
    > (after loading the tidyverse or just purrr)  

Well, no (to your "(....)") !

Functional programming is part of base R; no need to install any
tidy or untidy package : 

  a <- c(1, 4)
  b <- c(5, 8)

  unlist(  Map(`:`, a,b)  )

works perfectly.

... as does the also nice and simple (base R)
solution that  Tanvir Ahamed  already posted :

  unlist(as.vector(mapply(seq,a,b)))