Pontification :-)

  • If the data isn't right (especially if it contains not a number i.e. NA), then it won't work, especially with ggplot2.
  • If the data isn't right you won't get much of an error message. Use str(), head(), typeof() and really look at your data
  • Write the simplest possible test program to make sure your data is correct
  • You basically never need loops, yay! Hooray for apply(), sapply() et al