R help - May 2012 - use list as function arguments

Hello Folks,

Is there any way to pass a list into a function such that the function
will use the list as its arguments?  I haven't been able to figure that out.

The background: I'm trying to build a function that will apply another
function multiple times, each time with a different set of specified
arguments.  I'm trying to figure out how to pass in a list of argument
lists, then loop through the top-level list, passing in the lower-level
list as function arguments.

pseudocode:

b = list( list( arg1 = 1, arg2 = 2 ),
	  list( arg1 = 3, arg2 = 4 )
	)

a <- apply_function(arglist) {
	for (i in length(arglist)) {
		b(arglist[i])
	}
}


Specifically, the actual use I'm trying to implement is a function to
format columns of data frames and matrices independently.  What I have
so far is below, but it's not working.  Perhaps I'm going about this the
wrong way?


format_cols <- function(x, format_list = list()) {
    # usage: length(format_list) must equal ncol(x)
    #        format list should be a list of lists of key=value pairs
corresponding to format settings for each column

    if (is.data.frame(x)) {
        newout = data.frame()
    } else if (is.matrix(x)) {
        newout = matrix()
    }

    for (i in 1:ncol(x)){
        newout = cbind(newout, format(x,format_list[[i]]))
        x[,i] = format(x,format_list[[i]])
    }
    return(newout)
}

Thanks,
Allie

?do.call

On Thu, May 24, 2012 at 9:32 AM, Alexander Shenkin <ashenkin at ufl.edu>
wrote:
> Hello Folks,
>
> Is there any way to pass a list into a function such that the function
> will use the list as its arguments? ?I haven't been able to figure that
out.
>
> The background: I'm trying to build a function that will apply another
> function multiple times, each time with a different set of specified
> arguments. ?I'm trying to figure out how to pass in a list of argument
> lists, then loop through the top-level list, passing in the lower-level
> list as function arguments.
>
> pseudocode:
>
> b = list( list( arg1 = 1, arg2 = 2 ),
> ? ? ? ? ?list( arg1 = 3, arg2 = 4 )
> ? ? ? ?)
>
> a <- apply_function(arglist) {
> ? ? ? ?for (i in length(arglist)) {
> ? ? ? ? ? ? ? ?b(arglist[i])
> ? ? ? ?}
> }
>
>
> Specifically, the actual use I'm trying to implement is a function to
> format columns of data frames and matrices independently. ?What I have
> so far is below, but it's not working. ?Perhaps I'm going about
this the
> wrong way?
>
>
> format_cols <- function(x, format_list = list()) {
> ? ?# usage: length(format_list) must equal ncol(x)
> ? ?# ? ? ? ?format list should be a list of lists of key=value pairs
> corresponding to format settings for each column
>
> ? ?if (is.data.frame(x)) {
> ? ? ? ?newout = data.frame()
> ? ?} else if (is.matrix(x)) {
> ? ? ? ?newout = matrix()
> ? ?}
>
> ? ?for (i in 1:ncol(x)){
> ? ? ? ?newout = cbind(newout, format(x,format_list[[i]]))
> ? ? ? ?x[,i] = format(x,format_list[[i]])
> ? ?}
> ? ?return(newout)
> }
>
> Thanks,
> Allie
>
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-- 
Gregory (Greg) L. Snow Ph.D.
538280 at gmail.com