Expand delimited columns in R

A postdoctoral researcher asked me the other day to help him expand a vector of comma delimited values so he could do computations in R with it. I wrote an R function to solve the problem. Here is the before and after:

> data
  Name      Score1   Score2
1 Bill 1,3,4,3,6,9 F1,F3,F2
2  Bob       3,2,3 F2,F2,F4
3  Sam       2,5,3 F5,F2,F4
> expand.delimited(data)
   Name Score1
1  Bill      1
2  Bill      3
3  Bill      4
4  Bill      3
5  Bill      6
6  Bill      9
7   Bob      3
8   Bob      2
9   Bob      3
10  Sam      2
11  Sam      5
12  Sam      3
# Description
# Accepts a data.frame where col1 represents a factor and col2 represents
# comma or other delimited values to be expanded according to col1.
# Returns a data.frame.

# Usage
# expand.delimited(x, ...)

# Default
# expand.delimited(x, col1=1, col2=2, sep=",")

# Arguments
# x     A data.frame
# col1  Column in data.frame to act as factor
# col2  Column in data.frame that is delimited and will be expanded
# sep   Delimiter

#Download data
#Read in data 
data<-read.table("expand_delimited.txt",header=T)

#Function to expand data
expand.delimited <- function(x, col1=1, col2=2, sep=",") {
  rnum <- 1
  expand_row <- function(y) {
    factr <- y[col1]
    strng <- toString(y[col2])
    expand <- strsplit(strng, sep)[[1]]
    num <- length(expand)
    factor <- rep(factr,num)
    return(as.data.frame(cbind(factor,expand),
          row.names=seq(rnum:(rnum+num)-1)))
    rnum <- (rnum+num)-1
  }
  expanded <- apply(x,1,expand_row)
  df <- do.call("rbind", expanded)
  names(df) <- c(names(x)[col1],names(x)[col2])
  return(df)
}

# Example
expand.delimited(data)