A function to find the “Penultimax”

September 13, 2012

(This article was first published on Data and Analysis with R, at Work, and kindly contributed to R-bloggers)

Penulti-what? Let me explain: Today I had to iteratively go through each row of a donor history dataset and compare a donor’s maximum yearly donation total to the second highest yearly donation total. In even more concrete terms, for each row I had to compare the maximum value across 5 columns against the next highest number. This seemed to be a rather unique task, and so I had to make an R function to help carry it out.

So, I named the function “penultimax”, to honour the idea that it’s finding the second highest, or second max. It works pretty simply, really just by removing the maximum value from the input vector, and returning the maximum of the new vector, if it’s there at all. Following is the code for it (notice that it draws on an earlier function that I made, called safe.max, that returns an NA when it can’t find a maximum, instead of an error):

Did I miss something out there that’s simpler than what I wrote?