# R: Search the Help System

help.search {utils} | R Documentation

## 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.

### 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)

### 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 data bases 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.
`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 ‘RHOME/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 data base, or `NULL`.
`verbose` | logical; if `TRUE`, the search process is traced.
`rebuild` | a logical indicating whether the help data base 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`.

### Details

Upon installation of a package, a pre-built help.search index is serialized as ‘hsearch.rds’ in the ‘Meta’ directory. These files are used to create the data base.

The arguments `apropos` and `whatis` play a role similar to the Unix commands with the same names.

If possible, the help data base is saved in memory or (if memory limits have been set: see `mem.limits`) to a file in the session temporary directory for use by subsequent calls in the session.

Note that currently the aliases in the matching help files are not displayed.

### 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.
The internal format of the class is undocumented and subject to change.

### See Also

`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")
    ## 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")
    ## End(Not run)

[Package utils version 2.6.0 Index]