[R] A function like sum but with functions other than '+'
Joshua Wiley
jwiley.psych at gmail.com
Mon Apr 2 00:30:43 CEST 2012
Hi Sergio,
Look at ?Reduce
Cheers,
Josh
On Sun, Apr 1, 2012 at 3:25 PM, Julio Sergio <juliosergio at gmail.com> wrote:
> Because I didn't find in R any functions similar to the function 'reduce' from
> Python, I'm writing a function "freduce" as follows:
>
> freduce <- function(f, vec, ValIni=NULL, StopIn=NULL) {
> # f: is any function that takes two arguments of the same type
> # vec: is a vector of n values accepted by 'f'
> #
> # Initially f starts with ValIni, if it's given or the first element
> # of 'vec', and then applies sequentially f to that value and one of the
> # elements of 'vec', leaving the result as the first argument of 'f' for
> # the next application of the function.
> #
> # If StopIN is given, the result is compared with this value to stop the
> # operation and return such a value.
>
> # Detects if ValIni was given:
> r <- if (is.null(ValIni)) c(2,vec[1]) else c(1,ValIni)
> for (e in vec[r[1]:length(vec)]) {
> if (!is.null(StopIn) && r[2] == StopIn) return (StopIn)
> r[2] <- do.call(f, list(r[2],e))
> }
> return(r[2])
> }
>
> When this function is called with '+' and a vector of numbers, it behaves
> exactly as sum
>
> * freduce('+', c(3.5, 2.7, -1))
> [1] 5.2
> * sum(c(3.5, 2.7, -1))
> [1] 5.2
>
> But, then, you can call it with other operators; for instance, a generalized
> 'or' or 'and' operation, optionally stoping the operation when the value is
> determined:
>
> * freduce('|', c(0,0,1,0,0,1), StopIn=T)
> [1] TRUE
> * freduce('&', c(0,0,1,0,0,1), StopIn=F)
> [1] FALSE
>
> My question is if there exists a way to do this more directly in R?
>
> Thanks,
>
> --Sergio.
>
> ______________________________________________
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> 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.
--
Joshua Wiley
Ph.D. Student, Health Psychology
Programmer Analyst II, Statistical Consulting Group
University of California, Los Angeles
https://joshuawiley.com/
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