To make my code more readable, I like to avoid names of objects that already exist when creating new objects. Because of the package-based nature of R, and because functions are first-class objects, it can be easy to overwrite common functions that are not in base R (since a common package might use a short function name but without knowing what package to load there is no way to check for it). Objects such as the built-in logicals T and F also cause trouble.
Some examples that come to mind are:
One letter
- c
- t
- T/F
- J
Two letters
- df
A better solution might be to avoid using short names altogether in favor of more descriptive ones, and I generally try to do that as a matter of habit. Yet "df" for a function which manipulates a generic data.frame is plenty descriptive and a longer name adds little, so short names have their uses. In addition, for SO questions where the larger context isn't necessarily known, coming up with descriptive names is well-nigh impossible.
What other one- and two-letter variable names conflict with existing R objects? Which among those are sufficiently common that they should be avoided? If they are not in base, please list the package as well. The best answers will involve at least some code; please provide it if used.
Note that I am not asking whether or not overwriting functions that already exist is advisable or not. That question is addressed on SO already:
In R, what exactly is the problem with having variables with the same name as base R functions?
For visualizations of some answers here, see this question on CV:
https://stats.stackexchange.com/questions/13999/visualizing-2-letter-combinations