[R] Vector of functions

[Joshua Wiley]

Hi Thomas,

On Sat, Jul 2, 2011 at 9:36 AM, Thomas Stibor <thomas.stibor at in.tum.de> wrote:
> Hi there,
>
> I have a vector of some functions e.g.
> #-----------------------------#
> f.1 <- function(a) {
>  return( a );
> }
> f.2 <- function(a) {
>  return( 1 - (tanh(a))^2 );
> }
> f.3 <- function(a) {
>  return( 1 / (1+exp(-a)) * (1 - (1 / (1+exp(-a)))) );
> }
>
> func.l <- c(f.1, f.2, f.3);
> #-----------------------------#
>
> and would like to calculate the output value of a function in the
> vector, that is, pick e.g. function at position 2 in func.l and calculate the
> output value for a=42.
>
> func.l[2](42); # gives error

Almost there, you just need to use a different extraction operator...

func.l[[2]](42)

compare the output of

func.l[2]
func.l[[2]]

the first one retains the list structure, but just returns a list with
the second element of func.l, the second one actually returns a
function.  You can check this by looking at the class

class(func.l[2])
class(func.l[[2]])

Cheers,

Josh

>
> f <- func.l[2];
> f(42); # gives error
>
> Is there an easy way to solve this problem?
>
> Cheers,
>  Thomas
>
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>



-- 
Joshua Wiley
Ph.D. Student, Health Psychology
University of California, Los Angeles
http://www.joshuawiley.com/