R pitfalls #4: redefining the basics

I try to be economical when writing code; for example, I tend to use single quotes over double quotes for characters because it saves me one keystroke. One area where I don’t do that is when typing TRUE and FALSE (R accepts T and F as well), just because it is clearer to see in code and syntax highlighting kicks in. That’s why I was surprised to read Jason Morgan’s post in that it is possible to redefine T and F and get undesirable behavior.

Playing around it is quite easy to redefine other fundamental constants in R. For example, I posted in Twitter:

Ouch, dangerous! I tend to muck around with matrices quite a bit and, being a friend of parsimony, I often use capital letters to represent them. This would have eventually bitten me if I had used the abbreviated TRUE and FALSE. As Kevin Ushey replied to my tweet, one can redefine even basic functions like ‘+’ and be pure evil; over the top, sure, but possible.

Clown faces
Some times coding is scary (Photo: Luis).


  1. I was doing some Tukeys HSD results and innocently decided to call my vector letters, then wondered why my vector was 26 characters long rather than the 6 it should have been. Guess where R stores its alphabet! Easily done!

    1. R is a very large language with lots of reserved (although redefinable) keywords. It pays to pay attention all the time.

  2. Yeah,well, this is true in pretty much every language out there. Heck, I knew folks who thought it was funny to add this line to their coworkers’ .login file: “alias ls=logout” .

  3. I doubt that someone would change “pi”, but T and F might change by accidental reassignment.

    Running some error checking on at least the most common possibilities might be of use. I guess, though that these statements would have to come at the end of your script to make sure nothing was overwritten. Something along the lines of:

    if (!identical(T, TRUE)) stop("'T' has been reassigned to ", T)

    1. I doubt that someone would do it on purpose, but I can think of a number of acronyms related to my area of work for which it would make sense to use pi as a variable name.

    2. I’ve had some nasty bugs due to redefining T to a transition matrix in my early days of R programming; I was pretty annoyed when I found out the language would let me do something so dangerous.

  4. One redefinition in R is very useful for cross-platform work, e.g. when you are developing a script on a Mac but someone else will also be using it on Windows. This allows all the calls to quartz() to open a new graph window to still function on Windows (and could be easily swapped to go the other way):

    # when collaborating, need to swap windows() vs quartz() calls. This does that nicely:
    # (courtesy of https://stat.ethz.ch/pipermail/r-help/2008-December/181899.html)

    if(.Platform$OS.type==”windows”) {
    quartz<-function() windows()

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