Search the Help System
Description
Allows for searching the help system for documentation matching a given character string in the (file) name, alias, title, concept or keyword entries (or any combination thereof), using either fuzzy matching or regular expression matching. Names and titles of the matched help entries are displayed nicely formatted.
Vignette names, titles and keywords and demo names and titles may also be searched.
Usage
help.search(pattern, fields = c("alias", "concept", "title"),
apropos, keyword, whatis, ignore.case = TRUE,
package = NULL, lib.loc = NULL,
help.db = getOption("help.db"),
verbose = getOption("verbose"),
rebuild = FALSE, agrep = NULL, use_UTF8 = FALSE,
types = getOption("help.search.types"))
??pattern
field??pattern
Arguments
pattern
a character string to be matched in the specified
fields. If this is given, the arguments apropos,
keyword, and whatis are ignored.
fields
a character vector specifying the fields of the help
database to be searched. The entries must be abbreviations of
"name", "title", "alias", "concept", and
"keyword", corresponding to the help page's (file) name, its
title, the topics and concepts it provides documentation for, and
the keywords it can be classified to. See below for details and how
vignettes and demos are searched.
apropos
a character string to be matched in the help page topics and title.
keyword
a character string to be matched in the help page
‘keywords’. ‘Keywords’ are really categories: the
standard categories are listed in file ‘R.home("doc")/KEYWORDS’
(see also the example) and some package writers have defined their
own. If keyword is specified, agrep defaults to
FALSE.
whatis
a character string to be matched in the help page topics.
ignore.case
a logical. If TRUE, case is ignored during
matching; if FALSE, pattern matching is case sensitive.
package
a character vector with the names of packages to
search through, or NULL in which case all available
packages in the library trees specified by lib.loc are
searched.
lib.loc
a character vector describing the location of R
library trees to search through, or NULL. The default value
of NULL corresponds to all libraries currently known.
help.db
a character string giving the file path to a previously
built and saved help database, or NULL.
verbose
logical; if TRUE, the search process is traced.
Integer values are also accepted, with TRUE being equivalent
to 2, and 1 being less verbose. On Windows a progress
bar is shown during rebuilding, and on Unix a heartbeat is shown for
verbose = 1 and a package-by-package list for
verbose >= 2.
rebuild
a logical indicating whether the help database should
be rebuilt. This will be done automatically if lib.loc or
the search path is changed, or if package is used and a value
is not found.
agrep
if NULL (the default unless keyword is
used) and the character string to
be matched consists of alphanumeric characters, whitespace or a dash
only, approximate (fuzzy) matching via agrep is used
unless the string has fewer than 5 characters; otherwise, it is
taken to contain a regular expression to be matched via
grep . If FALSE, approximate matching is not
used. Otherwise, one can give a numeric or a list specifying the
maximal distance for the approximate match, see argument
max.distance in the documentation for agrep .
use_UTF8
logical: should results be given in UTF-8 encoding?
Also changes the meaning of regexps in agrep to be Perl regexps.
types
a character vector listing the types of documentation
to search. The entries must be abbreviations of "vignette"
"help" or "demo". Results will be presented in the
order specified.
field
a single value of fields to search.
Details
Upon installation of a package, a pre-built help.search index is
serialized as ‘hsearch.rds’ in the ‘Meta’ directory
(provided the package has any help pages). Vignettes are also
indexed in the ‘Meta/vignette.rds’ file. These files are used to
create the help search database via hsearch_db .
The arguments apropos and whatis play a role similar to
the Unix commands with the same names.
Searching with agrep = FALSE will be several times faster than
the default (once the database is built). However, approximate
searches should be fast enough (around a second with 5000 packages
installed).
If possible, the help database is saved in memory for use by subsequent calls in the session.
Note that currently the aliases in the matching help files are not displayed.
As with ? , in ?? the pattern may be prefixed with a
package name followed by :: or ::: to limit the search
to that package.
For help files, ‘\keyword’ entries which are not among the standard keywords as listed in file ‘KEYWORDS’ in the R documentation directory are taken as concepts. For standard keyword entries different from ‘internal’, the corresponding descriptions from file ‘KEYWORDS’ are additionally taken as concepts. All ‘\concept’ entries used as concepts.
Vignettes are searched as follows. The "name" and
"alias" are both the base of the vignette filename, and the
"concept" entries are taken from the ‘\VignetteKeyword’
entries. Vignettes are not classified using the help system
"keyword" classifications. Demos are handled
similarly to vignettes, without the "concept" search.
Value
The results are returned in a list object of class "hsearch",
which has a print method for nicely formatting the results of the
query. This mechanism is experimental, and may change in future
versions of R.
In R.app on macOS, this will show up a browser with selectable
items. On exiting this browser, the help pages for the selected items
will be shown in separate help windows.
The internal format of the class is undocumented and subject to change.
See Also
hsearch_db for more information on the help search
database employed, and for utilities to inspect available concepts and
keywords.
help ;
help.start for starting the hypertext (currently HTML)
version of R's online documentation, which offers a similar search
mechanism.
RSiteSearch to access an on-line search of R resources.
apropos uses regexps and has nice examples.
Examples
help.search("linear models") # In case you forgot how to fit linear
# models
help.search("non-existent topic")
??utils::help # All the topics matching "help" in the utils package
## Documentation with topic/concept/title matching 'print'
## (disabling fuzzy matching to not also match 'point')
help.search("print", agrep = FALSE)
help.search(apropos = "print", agrep = FALSE) # ignores concepts
## Help pages with documented topics starting with 'try':
help.search("^try", fields = "alias")
alias??"^try" # the same
## Help pages documenting high-level plots:
help.search(keyword = "hplot")
RShowDoc("KEYWORDS") # show all keywords