[R] Specifying argument values in a function

[Sam Albers]

Hello all,

I am trying write a fairly simple function that provide a quick way to
calculate several distributions for a data set. I am trying to provide
a function that has a argument that specifies which distribution is
outputted (here "norm" or "cumu"). I also have a melt argument but
that seems to be working fine. I have been able to get my function
working well for just one distribution but when I add another and try
to add a "dist.type" argument (with potential values "cumu" and
"norm"), I get an error message (see below). I am having trouble
finding material that explains how to add an argument that isn't a
TRUE/FALSE situation. Could any explain what I am doing wrong with the
second "distribution specifying" argument? I apologize as I am sure
this is a simple problem but I am just getting my feet wet with this
type of thing in R and am having a little trouble diagnosing the
problem.

#Example below:

library(reshape)

dat <- data.frame(`v1`=runif(6, 0, 125),
                  `v2`=runif(6, 50, 75),
                  `v3`=runif(6, 0, 100),
                  `v4`=runif(6, 0, 200)
                  )


my.norm <- function(x, melt=TRUE)
{
         #Normalized distribution
         N.dist <- as.data.frame(sapply(1:length(x), function(i)
(x[[i]]/rowSums(x[,c(1:4)]))*100 ))
         norm.melt <- melt.data.frame(N.dist)
         if (melt == TRUE) ##Default is a melted data frame
          return(norm.melt)
           if (melt == FALSE)
            return(N.dist)
       }

## So this single distribution function works fine
my.norm(dat, melt=TRUE)

my.fun <- function(x, melt=TRUE, dist.type=norm)
{
         #Normalized distribution
         N.dist <- as.data.frame(sapply(1:length(x), function(i)
(x[[i]]/rowSums(x[,c(1:4)]))*100 ))
         norm.melt <- melt.data.frame(N.dist)
         if (melt == TRUE && dist.type == norm) ##Default is a melted data frame
          return(norm.melt)
           if (melt == FALSE && dist.type == norm)
            return(N.dist)

         ## Cumulative distribution
         C.dist <- as.data.frame(t(apply(N.dist, 1, cumsum)))
         cumu.melt <- melt.data.frame(C.dist)
         if (melt == TRUE && dist.type == cumu) ##Default is a melted data frame
          return(cumu.melt)
           if (melt == FALSE && dist.type == cumu)
            return(C.dist)
       }

## But this function when used yields two different error messages
depending on the value used for dist.type:
my.fun(dat, melt=TRUE, dist.type = norm)
## Error in dist.type == norm :
##  comparison (1) is possible only for atomic and list types

my.fun(dat, melt=TRUE, dist.type = cumu)
## Error in my.fun(dat, dist.type = cumu) : object 'cumu' not found

Thanks in advance!

Sam