How to create a vector of functions?

Question

I would like to create a vector of functions using a two agruments function 'func', for instance this one:

func = function(number, coefficient) {  
     return(coefficient*number)  
}

here is how I create the vector of functions:

vector_of_functions = NULL  
for (i in 1:4) {  
     vector_of_functions = c(vector_of_functions, 
                             function(number) func(number=number, coefficient=i))  
}

My issue is that all functions that compose my vector are the same, even if they have been created using different i through the loop. It seams that they are evaluated using the last value of i (which is a global variable here).

Does anybody have an idea?

Answer 1

Use a factory function with a closure over its argument (which will hold the value of the looping variable):

> # the factory function
> makefunc <- function(x) { x; function() x }
> funclist <- list()
> for (i in 1:3) funclist[[i]] <- makefunc(i)
> funclist[[1]]()
[1] 1
> funclist[[2]]()
[1] 2
>