# [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.
>
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> 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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