What is your preferred style for naming variables in R?

Which conventions for naming variables and functions do you favor in R code?

As far as I can tell, there are several different conventions, all of which coexist in cacophonous harmony:

1. Use of period separator, e.g.

  stock.prices <- c(12.01, 10.12)
  col.names    <- c('symbol','price')

Pros: Has historical precedence in the R community, prevalent throughout the R core, and recommended by Google's R Style Guide.

Cons: Rife with object-oriented connotations, and confusing to R newbies

2. Use of underscores

  stock_prices <- c(12.01, 10.12)
  col_names    <- c('symbol','price')

Pros: A common convention in many programming langs; favored by Hadley Wickham's Style Guide, and used in ggplot2 and plyr packages.

Cons: Not historically used by R programmers; is annoyingly mapped to '<-' operator in Emacs-Speaks-Statistics (alterable with 'ess-toggle-underscore').

3. Use of mixed capitalization (camelCase)

  stockPrices <- c(12.01, 10.12)
  colNames    <- c('symbol','price')

Pros: Appears to have wide adoption in several language communities.

Cons: Has recent precedent, but not historically used (in either R base or its documentation).

Finally, as if it weren't confusing enough, I ought to point out that the Google Style Guide argues for dot notation for variables, but mixed capitalization for functions.

The lack of consistent style across R packages is problematic on several levels. From a developer standpoint, it makes maintaining and extending other's code difficult (esp. where its style is inconsistent with your own). From a R user standpoint, the inconsistent syntax steepens R's learning curve, by multiplying the ways a concept might be expressed (e.g. is that date casting function asDate(), as.date(), or as_date()? No, it's as.Date()).

Good previous answers so just a little to add here:

• underscores are really annoying for ESS users; given that ESS is pretty widely used you won't see many underscores in code authored by ESS users (and that set includes a bunch of R Core as well as CRAN authors, excptions like Hadley notwithstanding);

• dots are evil too because they can get mixed up in simple method dispatch; I believe I once read comments to this effect on one of the R list: dots are a historical artifact and no longer encouraged;

• so we have a clear winner still standing in the last round: camelCase. I am also not sure if I really agree with the assertion of 'lacking precendent in the R community'.

And yes: pragmatism and consistency trump dogma. So whatever works and is used by colleagues and co-authors. After all, we still have white-space and braces to argue about :)

I did a survey of what naming conventions that are actually used on CRAN that got accepted to the R Journal :) Here is a graph summarizing the results:

Turns out (no surprises perhaps) that lowerCamelCase was most often used for function names and period.separated names most often used for parameters. To use UpperCamelCase, as advocated by Google's R style guide is really rare however, and it is a bit strange that they advocate using that naming convention.

The full paper is here:

http://journal.r-project.org/archive/2012-2/RJournal_2012-2_Baaaath.pdf

Underscores all the way! Contrary to popular opinion, there are a number of functions in base R that use underscores. Run grep("^[^\\.]*$", apropos("_"), value = T) to see them all.

I use the official Hadley style of coding ;)

I like camelCase when the camel actually provides something meaningful -- like the datatype.

dfProfitLoss, where df = dataframe

or

vdfMergedFiles(), where the function takes in a vector and spits out a dataframe

While I think _ really adds to the readability, there just seems to be too many issues with using .-_ or other characters in names. Especially if you work across several languages.

This comes down to personal preference, but I follow the google style guide because it's consistent with the style of the core team. I have yet to see an underscore in a variable in base R.

As I point out here:

https://stackoverflow.com/questions/1232074/how-does-the-verbosity-of-identifiers-affect-the-performance-of-a-programmer/1239385#1239385

it's worth bearing in mind how understandable your variable names are to your co-workers/users if they are non-native speakers...

For that reason I'd say underscores and periods are better than capitalisation, but as you point out consistency is essential within your script.

As others have mentioned, underscores will screw up a lot of folks. No, it's not verboten but it isn't particularly common either.

Using dots as a separator gets a little hairy with S3 classes and the like.

In my experience, it seems like a lot of the high muckity mucks of R prefer the use of camelCase, with some dot usage and a smattering of underscores.

I have a preference for mixedCapitals.

But I often use periods to indicate what the variable type is:

mixedCapitals.mat is a matrix. mixedCapitals.lm is a linear model. mixedCapitals.lst is a list object.

and so on.

Usually I rename my variables using a ix of underscores and a mixed capitalization (camelCase). Simple variables are naming using underscores, example:

PSOE_votes -> number of votes for the PSOE (political group of Spain).

PSOE_states -> Categorical, indicates the state where PSOE wins {Aragon, Andalucia, ...)

PSOE_political_force -> Categorial, indicates the position between political groups of PSOE {first, second, third)

PSOE_07 -> Union of PSOE_votes + PSOE_states + PSOE_political_force at 2007 (header -> votes, states, position)

If my variable is a result of to applied function in one/two Variables I using a mixed capitalization.

Example:

positionXstates <- xtabs(~states+position, PSOE_07)