Create a vector of multiple series from two vectors

Question

I'm sure there is a super-simple solution to this, I just can't figure out what it is.

I have a long, single-variable dataset in R. I can identify the beginning and end of the multiple relevant ranges throughout, I just need to filter out the rest.

So given a vector x:

> x <- c(2400:2600)

And vectors of start points and end points:

> startpoints <- c(1,11,101)
> endpoints <- c(3,13,103)

I need to return the subset of x that looks like this:

> x[c(1:3, 11:13, 101:103)]
[1] 2400 2401 2402 2410 2411 2412 2500 2501 2502

I've tried this:

> x[startpoints:endpoints]

But R just takes the first value from each vector and returns that series:

[1] 2400 2401 2402

...with a couple of warnings

My startpoints and endpoints vectors should always be equal in length, although they may vary together in length with different datasets.

Answer 1

We can use mapply to get the sequence between corresponding elements of 'startpoints', 'endpoints' and this can subset the 'x' vector.

x[mapply(`:`, startpoints, endpoints)]
#[1] 2400 2401 2402 2410 2411 2412 2500 2501 2502

If the sequence are of different lengths, as @nicola mentioned, mapply returns a list , so we need to unlist it

x[unlist(mapply(`:`, startpoints, endpoints))]