Documentation

Description

These functions provide access to documentation. Documentation on a topic with name name (typically, an R object or a data set) can be printed with either help(name) or ?name.

Usage

help(topic, offline = FALSE, package = NULL,
     lib.loc = NULL, verbose = getOption("verbose"),
     try.all.packages = getOption("help.try.all.packages"),
     chmhelp = getOption("chmhelp"),
     htmlhelp = getOption("htmlhelp"),
     pager = getOption("pager"))

?topic

type?topic

Arguments

Details

topic is not optional: if it is omitted R will give a hint as to suitable topics if a package is specified, to available packages if lib.loc only is specified, and help on help itself if nothing is specified. (In all cases this will be text help.)

In the case of unary and binary operators and control-flow special forms (including if, for and function), the topic may need to be quoted.

If multiple help files matching topic are found, in interactive use a menu is presented for the user to choose one: otherwise the first on the search path is used. (The menu will be a graphical menu if possible if getOption("menu.graphics") is true, the default.)

If offline is TRUE, hardcopy of the documentation is produced by running the LaTeX version of the help page through latex (note that LaTeX 2e is needed). You need to customize the file ‘R_HOME/bin/helpPRINT.bat’ which contains an example. The appearance of the output can be customized through a file ‘Rhelp.cfg’ somewhere in your LaTeX search path.

If LaTeX versions of help pages were not built at the installation of the package, the print method will ask if conversion with R CMD Rdconv (which requires Perl) should be attempted.

S4 Method Documentation

The authors of formal (‘S4’) methods can provide documentation on specific methods, as well as overall documentation on the methods of a particular function. The "?" operator allows access to this documentation in three ways.

The expression methods ? f will look for the overall documentation methods for the function f. Currently, this means the documentation file containing the alias f-methods.

There are two different ways to look for documentation on a particular method. The first is to supply the topic argument in the form of a function call, omitting the type argument. The effect is to look for documentation on the method that would be used if this function call were actually evaluated. See the examples below. If the function is not a generic (no S4 methods are defined for it), the help reverts to documentation on the function name.

The "?" operator can also be called with type supplied as "method"; in this case also, the topic argument is a function call, but the arguments are now interpreted as specifying the class of the argument, not the actual expression that will appear in a real call to the function. See the examples below.

The first approach will be tedious if the actual call involves complicated expressions, and may be slow if the arguments take a long time to evaluate. The second approach avoids these difficulties, but you do have to know what the classes of the actual arguments will be when they are evaluated.

Both approaches make use of any inherited methods; the signature of the method to be looked up is found by using selectMethod (see the documentation for getMethod).

Note

Unless lib.loc is specified explicitly, the loaded packages are searched before those in the specified libraries. This ensures that if a library is loaded from a library not in the known library trees, then the help from the loaded library is used. If lib.loc is specified explicitly, the loaded packages are not searched.

If this search fails and argument try.all.packages is TRUE and neither packages nor lib.loc is specified, then all the packages in the known library trees are searched for help on topic and a list of (any) packages where help may be found is printed (but no help is shown). N.B. searching all packages can be slow.

The help files can be many small files. On some file systems it is desirable to save space, and the text files in the ‘help’ directory of an installed package can be zipped up as a zip archive ‘Rhelp.zip’. Ensure that file ‘AnIndex’ remains un-zipped. Similarly, all the files in the ‘latex’ directory can be zipped to ‘Rhelp.zip’. This is done on Windows for the larger packages.

References

Becker, R. A., Chambers, J. M. and Wilks, A. R. (1988) The New S Language. Wadsworth & Brooks/Cole.

See Also

help.search() for finding help pages on a “vague” topic; help.start() which opens the HTML version of the R help pages; library() for listing available packages and the user-level objects they contain; data() for listing available data sets; methods().

See prompt() to get a prototype for writing help pages of private packages.

Examples

help()
help(help)              # the same

help(lapply)
?lapply                 # the same

help("for")             # or ?"for", but the quotes are needed
?"+"

help(package="splines") # get help even when package is not loaded

data()                  # list all available data sets
?women                  # information about data set "women"

topi <- "women"
## Not run: help(topi) ##--> Error: No documentation for 'topi'

try(help("bs", try.all.packages=FALSE)) # reports not found (an error)
help("bs", try.all.packages=TRUE) # reports can be found in package 'splines'

## Not run: 
require(methods)
## define a S4 generic function and some methods
combo <- function(x, y) c(x, y)
setGeneric("combo")
setMethod("combo", c("numeric", "numeric"), function(x, y) x+y)

## assume we have written some documentation for combo, and its methods ....

?combo  ## produces the function documentation

methods?combo  ## looks for the overall methods documentation

method?combo("numeric", "numeric")  ## documentation for the method above

?combo(1:10, rnorm(10))  ## ... the same method, selected according to
                         ## the arguments (one integer, the other numeric)

?combo(1:10, letters)    ## documentation for the default method
## End(Not run)