“unpacking” a factor list from a data.frame

Question

I\'m new to R / having the option to easily re-organize data, and have hunted around for a solution but can\'t find exactly what I\'d like to do. Reshape2\'s melt/cast doesn

Answer 1

A possibility:

x <- read.table(textConnection('
    ID      category_list    xval    yval
     ID1   "cat1, cat2, cat3"   xnum1   ynum1
     ID2         "cat2, cat3"   xnum2   ynum2
     ID3               "cat1"   xnum3   ynum3'),
          header=TRUE,stringsAsFactors=FALSE)

library(plyr)
ddply(x,"ID",transform,category=strsplit(category_list,",")[[1]])

##    ID    category_list  xval  yval category
## 1 ID1 cat1, cat2, cat3 xnum1 ynum1     cat1
## 2 ID1 cat1, cat2, cat3 xnum1 ynum1     cat2
## 3 ID1 cat1, cat2, cat3 xnum1 ynum1     cat3
## 4 ID2       cat2, cat3 xnum2 ynum2     cat2
## 5 ID2       cat2, cat3 xnum2 ynum2     cat3