Is there anything like cumsum and cumprod but which allows you to
apply an arbitrary function instead of sum and product? In other words,
I want a function cumfunc(x, f) that returns a vector, so that for all n
up to the length of x
cumapply(x,f)[n] = f(x[1:n])
This would give cumsum and cumprod as special cases when f=sum or
f=prod.
I could write such a function, but I can't see a way to do it
without a loop, so I'm wondering if such a function exists that may be
speedier.
Thanks,
--
--OKB (not okblacke)
Brendan Barnwell
"Do not follow where the path may lead. Go, instead, where there is
no path, and leave a trail."
--author unknown
?Reduce maybe HTH, baptiste 2009/9/16 OKB (not okblacke) <brenbarn@brenbarn.net>> Is there anything like cumsum and cumprod but which allows you to > apply an arbitrary function instead of sum and product? In other words, > I want a function cumfunc(x, f) that returns a vector, so that for all n > up to the length of x > > cumapply(x,f)[n] = f(x[1:n]) > > This would give cumsum and cumprod as special cases when f=sum or > f=prod. > > I could write such a function, but I can't see a way to do it > without a loop, so I'm wondering if such a function exists that may be > speedier. > > Thanks, > -- > --OKB (not okblacke) > Brendan Barnwell > "Do not follow where the path may lead. Go, instead, where there is > no path, and leave a trail." > --author unknown > > ______________________________________________ > R-help@r-project.org mailing list > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide > http://www.R-project.org/posting-guide.html > and provide commented, minimal, self-contained, reproducible code. >[[alternative HTML version deleted]]
On Sep 16, 2009, at 5:00 PM, OKB (not okblacke) wrote:> Is there anything like cumsum and cumprod but which allows you to > apply an arbitrary function instead of sum and product? In other > words, > I want a function cumfunc(x, f) that returns a vector, so that for > all n > up to the length of x > > cumapply(x,f)[n] = f(x[1:n])?Reduce Slightly modified from the help page: > add <- function(x) Reduce("+", x, accumulate=TRUE) > add(list(1, 2, 3)) [1] 1 3 6 > cummult <- function(x) Reduce("*", x, accumulate=TRUE) > cummult(list(1, 2, 3)) [1] 1 2 6> > This would give cumsum and cumprod as special cases when f=sum or > f=prod. > > I could write such a function, but I can't see a way to do it > without a loop, so I'm wondering if such a function exists that may be > speedier.-- David Winsemius, MD Heritage Laboratories West Hartford, CT