What does “S3 methods” mean in R?

by

Most of the relevant information can be found by looking at ?S3 or ?UseMethod, but in a nutshell:

S3 refers to a scheme of method dispatching. If you’ve used R for a while, you’ll notice that there are print, predict and summary methods for a lot of different kinds of objects.

In S3, this works by:

  • setting the class of objects of
    interest (e.g.: the return value of a
    call to method glm has class glm)
  • providing a method with the general
    name (e.g. print), then a dot, and
    then the classname (e.g.:
    print.glm)
  • some preparation has to have been
    done to this general name (print)
    for this to work, but if you’re
    simply looking to conform yourself to
    existing method names, you don’t need
    this (see the help I refered to
    earlier if you do).

To the eye of the beholder, and particularly, the user of your newly created funky model fitting package, it is much more convenient to be able to type predict(myfit, type="class") than predict.mykindoffit(myfit, type="class").

There is quite a bit more to it, but this should get you started. There are quite a few disadvantages to this way of dispatching methods based upon an attribute (class) of objects (and C purists probably lie awake at night in horror of it), but for a lot of situations, it works decently. With the current version of R, newer ways have been implemented (S4 and reference classes), but most people still (only) use S3.

More Related Contents:

  1. Collapse / concatenate / aggregate a column to a single comma separated string within each group
  2. Filter data.frame rows by a logical condition
  3. Find complement of a data frame (anti – join)
  4. Subset data frame based on number of rows per group
  5. Evaluate expression given as a string
  6. Pass a data.frame column name to a function
  7. Drop data frame columns by name
  8. What is the difference between require() and library()?
  9. How to sort a character vector where elements contain letters and numbers in R?
  10. Plot two graphs in same plot in R
  11. Add column which contains binned values of a numeric column
  12. Replace all 0 values to NA
  13. How to find common elements from multiple vectors?
  14. Using R to download zipped data file, extract, and import data
  15. Generate multiple graphics from within an R function
  16. How does one reorder columns in a data frame?
  17. Scheduling R Script
  18. Calculate group mean, sum, or other summary stats. and assign column to original data
  19. What are the main differences between R data files?
  20. What are the differences between “=” and “
  21. Finding All Positions for Multiple Elements in a Vector
  22. Get filename without extension in R
  23. ending “+” prompt in R
  24. R round to nearest .5 or .1
  25. What do the %op% operators in mean? For example “%in%”?
  26. How to subtract years?
  27. Create categorical variable in R based on range
  28. Apply several summary functions (sum, mean, etc.) on several variables by group in one call
  29. Order of operator precedence when using “:” (the colon)
  30. How can I read the source code for an R function?

Leave a Comment