On Dec 10, 2012, at 1:29 PM, Sam Steingold <s...@gnu.org> wrote:
> How do I sum portions of a vector into another vector?
> E.g., for
> --8<---------------cut here---------------start------------->8---
>> vec <- 1:10
>> breaks <- c(3,8,10)
> --8<---------------cut here---------------end--------------->8---
> I want to get a vector of length 3 with content
> --8<---------------cut here---------------start------------->8---
> 6 = 1+2+3
> 30 = 4+5+6+7+8
> 19 = 9+10
> --8<---------------cut here---------------end--------------->8---
> Obviously, I could write a loop, but I would rather have a vectorized
> version.
> Thanks!
See ?findInterval.
> findInterval(seq(along = vec), breaks + 1)
[1] 0 0 0 1 1 1 1 1 2 2
> as.vector(sapply(split(vec, findInterval(seq(along = vec), breaks + 1)),
sum))
[1] 6 30 19
Did you just want the above, or did you really want:
> as.vector(sapply(split(vec, findInterval(seq(along = vec), breaks + 1)),
function(x) paste(sum(x), "=", paste(x, collapse = "+"))))
[1] "6 = 1+2+3" "30 = 4+5+6+7+8" "19 = 9+10"
Regards,
Marc Schwartz
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