help.search
Search the Help System
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.
- Keywords
- documentation
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
, andwhatis
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. Ifkeyword
is specified,agrep
defaults toFALSE
.- whatis
a character string to be matched in the help page topics.
- ignore.case
a logical. If
TRUE
, case is ignored during matching; ifFALSE
, 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 bylib.loc
are searched.- lib.loc
a character vector describing the location of R library trees to search through, or
NULL
. The default value ofNULL
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, withTRUE
being equivalent to2
, and1
being less verbose. On Windows a progress bar is shown during rebuilding, and on Unix a heartbeat is shown forverbose = 1
and a package-by-package list forverbose >= 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 ifpackage
is used and a value is not found.- agrep
if
NULL
(the default unlesskeyword
is used) and the character string to be matched consists of alphanumeric characters, whitespace or a dash only, approximate (fuzzy) matching viaagrep
is used unless the string has fewer than 5 characters; otherwise, it is taken to contain a regular expression to be matched viagrep
. IfFALSE
, approximate matching is not used. Otherwise, one can give a numeric or a list specifying the maximal distance for the approximate match, see argumentmax.distance
in the documentation foragrep
.- 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
library(utils)
# NOT RUN {
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
# }
# NOT RUN {
help.search("print") # All help pages with topics or title
# matching 'print'
help.search(apropos = "print") # The same
help.search(keyword = "hplot") # All help pages documenting high-level
# plots.
file.show(file.path(R.home("doc"), "KEYWORDS")) # show all keywords
## Help pages with documented topics starting with 'try'.
help.search("\\btry", fields = "alias")
# }