Accessing R Source
2017-07-31 update: Since I wrote this @jimhester has created the lookup package to automate this process. So if all you want is the result, just use that! If you want a bit more context, then keep reading. AFAIK this info is still fundamentally sound.
How to get at R source. I am sick of Googling this. I am writing it down this time.
TL;DR
methods(<S3_GENERIC>)
<S3_GENERIC>.default
<S3_GENERIC>.<CLASS>
getAnywhere(<S3_GENERIC>.<CLASS>)
getS3method("<S3_GENERIC>", "<CLASS>")
<NAMESPACE>:::<S3_GENERIC>.<CLASS>References
The definitive reference is this classic R News article:
Accessing the Sources
Uwe Ligges
https://cran.r-project.org/doc/Rnews/Rnews_2006-4.pdf
Volume 6/4, October 2006. Go to page 43.
Another good reference is the help file for method():
https://stat.ethz.ch/R-manual/R-patched/library/utils/html/methods.html
Just print it
If you are lucky, just printing the function will work.
setNames
#> function (object = nm, nm)
#> {
#> names(object) <- nm
#> object
#> }
#> <bytecode: 0x7fce93c98920>
#> <environment: namespace:stats>But there are many ways this can fail.
vector # .Internal
#> function (mode = "logical", length = 0L)
#> .Internal(vector(mode, length))
#> <bytecode: 0x7fce94835c40>
#> <environment: namespace:base>
class # .Primitive
#> function (x) .Primitive("class")
subset # S3 generic
#> function (x, ...)
#> UseMethod("subset")
#> <bytecode: 0x7fce933c0178>
#> <environment: namespace:base>What then?
Function is an S3 generic
These are characterized by UseMethod() in the printed result:
subset
#> function (x, ...)
#> UseMethod("subset")
#> <bytecode: 0x7fce933c0178>
#> <environment: namespace:base>Print the default method by appending .default:
subset.default
#> function (x, subset, ...)
#> {
#> if (!is.logical(subset))
#> stop("'subset' must be logical")
#> x[subset & !is.na(subset)]
#> }
#> <bytecode: 0x7fce935f1228>
#> <environment: namespace:base>Or list the methods for this generic:
methods(subset)
#> [1] subset.data.frame subset.default subset.matrix
#> see '?methods' for accessing help and source codeThen print the method you seek:
subset.matrix
#> function (x, subset, select, drop = FALSE, ...)
#> {
#> if (missing(select))
#> vars <- TRUE
#> else {
#> nl <- as.list(1L:ncol(x))
#> names(nl) <- colnames(x)
#> vars <- eval(substitute(select), nl, parent.frame())
#> }
#> if (missing(subset))
#> subset <- TRUE
#> else if (!is.logical(subset))
#> stop("'subset' must be logical")
#> x[subset & !is.na(subset), vars, drop = drop]
#> }
#> <bytecode: 0x7fce93314388>
#> <environment: namespace:base>Sometimes the method definition is not exported from the package namespace. That's indicated by an asterisk * in the listing (pardon the way I do this, but I have to send through capture.output() if the asterisks are to survive tail():
mout <- capture.output(methods(print))
tail(mout)
#> [1] "[195] print.vignette* "
#> [2] "[196] print.warnings "
#> [3] "[197] print.xgettext* "
#> [4] "[198] print.xngettext* "
#> [5] "[199] print.xtabs* "
#> [6] "see '?methods' for accessing help and source code"Good news: you've found the function you need. Bad news: you still can't read the source.
print.xgettext
#> Error in eval(expr, envir, enclos): object 'print.xgettext' not foundUse getAnywhere() or getS3method() to close the deal:
getAnywhere(print.xgettext)
#> A single object matching 'print.xgettext' was found
#> It was found in the following places
#> registered S3 method for print from namespace tools
#> namespace:tools
#> with value
#>
#> function (x, ...)
#> {
#> cat(x, sep = "\n")
#> invisible(x)
#> }
#> <bytecode: 0x7fce9787e150>
#> <environment: namespace:tools>This printed the source AND we learned the associated namespace. If you know the namespace, you can also use ::: to see source:
tools:::print.xgettext
#> function (x, ...)
#> {
#> cat(x, sep = "\n")
#> invisible(x)
#> }
#> <bytecode: 0x7fce9787e150>
#> <environment: namespace:tools>Compiled code
Whenever you see .C(), .Call(), .Fortran(), .External(), or .Internal() and .Primitive(), the source you seek is in underlying compiled code.
You need to locate the source code of R or the associated add-on package on the internet or download it locally. Then browse around or search.
Visit the source of R on the internet:
- A read-only mirror of the R source on GitHub: https://github.com/wch/r-source
- A rudimentary web interface is available from the SVN repository: https://svn.r-project.org/R/.
Download source of R itself:
-
Download source for current release from https://cran.r-project.org, e.g.
R-3.2.2.tar.gz, and unpack it.tar xvf R-3.2.2.tar.gz -
See more info there about getting the development version.
-
Or checkout from the official Subversion repository https://svn.r-project.org/R/.
How to find what you need in the R source (paraphrasing Ligges, in places):
- For R and standard R packages, look in subdirs of
$R_HOME/src/, most especially$R_HOME/src/main/. - If calling R function is
.Primitive()or.Internal(), find the entry point$R HOME/src/main/names.c. Then try to find that function. Example below. - Use the GitHub search capabilities.
Example: I want the source for levels<-.
`levels<-` # .Primitive()
#> function (x, value) .Primitive("levels<-")Search for levels<- in $R HOME/src/main/names.c and we find this line:
{"levels<-", do_levelsgets, 0, 1, 2, {PP_FUNCALL, PREC_LEFT, 1}}which tells us we're looking for do_levelsgets. Now use your search capability (GitHub? grep?) to look for that within the files below $R_HOME/src/. I choose the GitHub option and use this query:
do_levelsgets path:src/mainAnd finally arrive at my destination: lines 1242 through 1261 in $R_HOME/src/main/attrib.c.
Visit the source of an R package on the internet:
- If developed on GitHub, go to package's official repo. Ideally, this will be provided as a URL on the package's CRAN page, but sadly not always the case.
- Example: https://github.com/vegandevs/vegan
- If the package is on CRAN but not on GitHub, go to the read-only mirror of its source from the METACRAN project.
- Example: https://github.com/cran/MASS
Download source of an add-on package:
-
Visit the package on CRAN, e.g., https://cran.r-project.org/web/packages/vegan/index.html, download the
*.tar.gzlinked from "Package source", and unpack it.tar xvf vegan_2.3-1.tar.gz -
If developed on GitHub, e.g., https://github.com/vegandevs/vegan, download via the "Download ZIP" button or Git clone it.
git clone https://github.com/vegandevs/vegan.git
How to find what you need in R package source:
- Look in the
srcdirectory. If you are lucky, there will be a file that obviously contains the function of interest. - Otherwise, search with
grep, your editor/IDE, or GitHub queries and follow the trail to rainbow's end.
Example: I want the source for dplyr::bind_rows. dplyr is developed on GitHub.
First I search within the R directory with this GitHub search query:
bind_rows path:RGitHub search only shows you the first one or two matches within a file, but I gather that R/bind.r is where I want to look. I visit it in the browser and use the browser to search for bind_rows, which reveals the function definition. That reveals I actually need bind_rows_.
So I do another GitHub search with this query:
bind_rows_which reveals hits in
R/bind.r
R/RcppExports.R
src/bind.cpp
src/RcppExports.cpp
Reading the relevant bit of src/bind.cpp reveals I really need rbind__impl.
So I do another GitHub search with this query:
rbind__implAnd finally arrive at my destination: lines 7 though 119 of src/bind.cpp.
Things I haven't covered
An incomplete list:
- S4
- Other places to put code, e.g. R-Forge or BitBucket