help {utils} | R Documentation |
Documentation
Description
help
is the primary interface to the help systems.
Usage
help(topic, package = NULL, lib.loc = NULL,
verbose = getOption("verbose"),
try.all.packages = getOption("help.try.all.packages"),
help_type = getOption("help_type"))
Arguments
topic |
usually, a name or character string specifying the topic for which help is sought. A character string (enclosed in explicit single or double quotes) is always taken as naming a topic. If the value of See ‘Details’ for what happens if this is omitted. |
package |
a name or character vector giving the packages to look
into for documentation, or |
lib.loc |
a character vector of directory names of R libraries,
or |
verbose |
logical; if |
try.all.packages |
logical; see |
help_type |
character string: the type of help required.
Possible values are |
Details
The following types of help are available:
Plain text help
HTML help pages with hyperlinks to other topics, shown in a browser by
browseURL
.
(On Unix-alikes, where possible an existing browser window is re-used: the macOS GUI uses its own browser window.)If for some reason HTML help is unavailable (see
startDynamicHelp
), plain text help will be used instead.For
help
only, typeset as PDF – see the section on ‘Offline help’.
- On Unix-alikes:
-
The ‘factory-fresh’ default is text help except from the macOS GUI, which uses HTML help displayed in its own browser window.
- On Windows:
-
The default for the type of help is selected when R is installed – the ‘factory-fresh’ default is HTML help.
The rendering of text help will use directional quotes in suitable
locales (UTF-8 and single-byte Windows locales): sometimes the fonts
used do not support these quotes so this can be turned off by setting
options(useFancyQuotes = FALSE)
.
topic
is not optional: if it is omitted R will give
If a package is specified, (text or, in interactive use only, HTML) information on the package, including hints/links to suitable help topics.
If
lib.loc
only is specified, a (text) list of available packages.Help on
help
itself if none of the first three arguments is specified.
Some topics need to be quoted (by backticks) or given as a
character string. These include those which cannot syntactically
appear on their own such as unary and binary operators,
function
and control-flow reserved words (including
if
, else
for
, in
, repeat
,
while
, break
and next
). The other reserved
words can be used as if they were names, for example TRUE
,
NA
and Inf
.
If multiple help files matching topic
are found, in interactive
use a menu is presented for the user to choose one: in batch use the
first on the search path is used. (For HTML help the menu will be an
HTML page, otherwise a graphical menu if possible if
getOption("menu.graphics")
is true, the default.)
Note that HTML help does not make use of lib.loc
: it will
always look first in the loaded packages and then along
.libPaths()
.
Offline help
Typeset documentation is produced by running the LaTeX version of the
help page through pdflatex
: this will produce a PDF file.
The appearance of the output can be customized through a file
‘Rhelp.cfg’ somewhere in your LaTeX search path: this will be
input as a LaTeX style file after Rd.sty
. Some
environment variables are consulted, notably R_PAPERSIZE
(via getOption("papersize")
) and R_RD4PDF (see
‘Making manuals’ in the
‘R Installation and Administration’ manual).
If there is a function offline_help_helper
in the workspace or
further down the search path it is used to do the typesetting,
otherwise the function of that name in the utils
namespace (to
which the first paragraph applies). It should accept at least two
arguments, the name of the LaTeX file to be typeset and the type
(which is nowadays ignored). It accepts a third argument,
texinputs
, which will give the graphics path when the help
document contains figures, and will otherwise not be supplied.
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 displayed (with hyperlinks for
help_type = "html"
).
NB: searching all packages can be slow, especially
the first time (caching of files by the OS can expedite subsequent
searches dramatically).
References
Becker, R. A., Chambers, J. M. and Wilks, A. R. (1988) The New S Language. Wadsworth & Brooks/Cole.
See Also
?
for shortcuts to help topics.
help.search()
or ??
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
help objects they contain;
data()
for listing available data sets;
methods()
.
Use prompt()
to get a prototype for writing help
pages of your own package.
Examples
help()
help(help) # the same
help(lapply)
help("for") # or ?"for", but quotes/backticks are needed
try({# requires working TeX installation:
help(dgamma, help_type = "pdf")
## -> nicely formatted pdf -- including math formula -- for help(dgamma):
system2(getOption("pdfviewer"), "dgamma.pdf", wait = FALSE)
})
help(package = "splines") # get help even when package is not loaded
topi <- "women"
help(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'
## For programmatic use:
topic <- "family"; pkg_ref <- "stats"
help((topic), (pkg_ref))