For each row in an R dataframe

Question

I have a dataframe, and for each row in that dataframe I have to do some complicated lookups and append some data to a file.

The dataFrame contains scientific results for selected wells from 96 well plates used in biological research so I want to do something like:

for (well in dataFrame) {
  wellName <- well$name    # string like "H1"
  plateName <- well$plate  # string like "plate67"
  wellID <- getWellID(wellName, plateName)
  cat(paste(wellID, well$value1, well$value2, sep=","), file=outputFile)
}

In my procedural world, I'd do something like:

for (row in dataFrame) {
    #look up stuff using data from the row
    #write stuff to the file
}

What is the "R way" to do this?

Answer 1

You can use the by() function:

by(dataFrame, seq_len(nrow(dataFrame)), function(row) dostuff)

But iterating over the rows directly like this is rarely what you want to; you should try to vectorize instead. Can I ask what the actual work in the loop is doing?