[R] summing elements in a list of functions

[Peter Dalgaard]

James Foadi <jf117 at york.ac.uk> writes:

> Dear all,
> I have looked for an answer for a couple of days, but can't come with any 
> solution.
> 
> I have a set of functions, say:
> 
> > t0 <- function(x) {1}
> > t1 <- function(x) {x}
> > t2 <- function(x) {x^2}
> > t3 <- function(x) {x^3}
> 
> I would like to find a way to add up the previous 4 functions and obtain a new 
> function:
> 
> > rrr <- function(x) {1+x+x^2+x^3}
> 
> without, actually, having to write it in the previous form (I could have cases 
> with hundreds of functions). I thought that perhaps I could first define a 
> list of functions:
> 
> > ttt <- list(t0,t1,t2,t3)
> 
> and then I could use something like "sum", to add up all the elements of the 
> list and obtain another function. I've tried:
> 
> > rrr <- function(x) {sum(ttt)}
> 
> but it does not work.
> 
> Any help with this is greatly appreciated.

rrr <- function(x) sum(sapply(ttt,function(f)f(x)))

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   O__  ---- Peter Dalgaard             Øster Farimagsgade 5, Entr.B
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