I'll add my suggestion, which first extracts from x the elements
up to but not including the first positive one and then sums them:
f3 <- function(x) { sum(x[cumsum(x>0) == 0]) }
Michaels suggestion was
sum(x[seq_len(which.max(x > 0)])
but that includes the first positive element so I think it should be
at least
f1 <- function(x) sum(x[seq_len(which.max(x>0)-1)])
(but that still fails in some cases).
Jeff's was
f2 <- function (x) {
tmp <- aggregate(x, list(lvl = cumsum(abs(diff(c(FALSE, x > 0))))), FUN =
sum)
tmp[0 == tmp$lvl, "x"]
}
To test them, make a list of datasets
> xs <- list(allNeg=c(-1, -3, -9), allPos=c(1,3,9), firstPos=c(1,-3,-9),
> firstNeg=c(-1,-3,+9), misc=c(-1,-3,9,-27,-81))
> sapply(xs, function(x)try(f1(x)))
allNeg allPos firstPos firstNeg misc
0 0 0 -4 -4
> sapply(xs, function(x)try(f2(x)))
$allNeg
[1] -13
$allPos
numeric(0)
$firstPos
numeric(0)
$firstNeg
[1] -4
$misc
[1] -4
> sapply(xs, function(x)try(f3(x)))
allNeg allPos firstPos firstNeg misc
-13 0 0 -4 -4
Bill Dunlap
Spotfire, TIBCO Software
wdunlap tibco.com
> -----Original Message-----
> From: r-help-boun...@r-project.org [mailto:r-help-boun...@r-project.org] On
> Behalf
> Of Jeff Newmiller
> Sent: Tuesday, August 07, 2012 10:25 AM
> To: R. Michael Weylandt; number10
> Cc: r-help@r-project.org
> Subject: Re: [R] Sum of vector elements
>
> Another approach... not exactly more direct, but perhaps more robust and more
> general:
>
> tmp <- aggregate(x,list(lvl=cumsum(abs(diff(c(FALSE,x>0))))), FUN=sum)
> ans <- tmp[0==tmp$lvl,"x"]
>
> abs(diff()) finds transitions, FALSE forces level zero to represent negative
> numbers
> cumsum marks levels (groups of positive and not-positive numbers)
> aggregate does the summation
> ans may be empty if x started with positive numbers.
> ---------------------------------------------------------------------------
> Jeff Newmiller The ..... ..... Go Live...
> DCN:<jdnew...@dcn.davis.ca.us> Basics: ##.#. ##.#. Live Go...
> Live: OO#.. Dead: OO#.. Playing
> Research Engineer (Solar/Batteries O.O#. #.O#. with
> /Software/Embedded Controllers) .OO#. .OO#. rocks...1k
> ---------------------------------------------------------------------------
> Sent from my phone. Please excuse my brevity.
>
> "R. Michael Weylandt" <michael.weyla...@gmail.com> wrote:
>
> >I'd do something like this:
> >
> >x <- sample(seq(-10, 10))
> >
> >sum(x[seq_len(which.max(x > 0)])
> >
> >Though others might have more direct solutions.
> >
> >which.max() gets you the index of the first time x > 0 -- seq_len
> >gives you numbers 1 to that index -- then just subset and sum like
> >normal.
> >
> >Best,
> >Michael
> >
> >On Tue, Aug 7, 2012 at 7:37 AM, number10 <havana_dr...@ymail.com>
> >wrote:
> >> Hi, Is it possible to avoid using do and while loops to calculate the
> >sum of
> >> the elements of a vector until the appearance of the first positive
> >element.
> >>
> >>
> >>
> >> --
> >> View this message in context:
> >http://r.789695.n4.nabble.com/Sum-of-vector-elements-tp4639395.html
> >> Sent from the R help mailing list archive at Nabble.com.
> >>
> >> ______________________________________________
> >> R-help@r-project.org mailing list
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> >> PLEASE do read the posting guide
> >http://www.R-project.org/posting-guide.html
> >> and provide commented, minimal, self-contained, reproducible code.
> >
> >______________________________________________
> >R-help@r-project.org mailing list
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> >PLEASE do read the posting guide
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> >and provide commented, minimal, self-contained, reproducible code.
>
> ______________________________________________
> R-help@r-project.org mailing list
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> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
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