help                  package:utils                  R Documentation

_D_o_c_u_m_e_n_t_a_t_i_o_n

_D_e_s_c_r_i_p_t_i_o_n:

     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'.

_U_s_a_g_e:

     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

_A_r_g_u_m_e_n_t_s:

   topic: usually, the name on which documentation is sought. The name
          may be quoted or unquoted (but note that if 'topic' is the
          name of a variable containing a character string
          documentation is provided for the name, not for the character
          string).

          The 'topic' argument may also be a function call, to ask for
          documentation on a corresponding method.  See the section on
          method documentation.

          See Details for what happens if this is omitted. 

 offline: a logical indicating whether documentation should be
          displayed on-line to the screen (the default) or hardcopy of
          it should be produced.

 package: a name or character vector giving the packages to look into
          for documentation, or 'NULL'.  By default, all packages in
          the search path are used.

 lib.loc: a character vector of directory names of R libraries, or
          'NULL'.  The default value of 'NULL' corresponds to all
          libraries currently known.  If the default is used, the
          loaded packages are searched before the libraries.

 verbose: logical; if 'TRUE', the file name is reported.

try.all.packages: logical; see 'Note'.

 chmhelp: logical (or 'NULL'). Only relevant under Windows. If 'TRUE'
          the Compiled HTML version of the help on the topic will be
          shown in a help viewer.

htmlhelp: logical (or 'NULL').  If 'TRUE' (which is the default after
          'help.start' has been called), the HTML version of the help
          on the topic will be shown in the browser specified by
          'options("browser")'.  See 'browseURL' for details of the
          browsers that are supported.  Where possible an existing
          browser window is re-used.

   pager: the pager to be used for 'file.show'.

    type: the special type of documentation to use for this topic; for
          example, if the type is 'class', documentation is provided
          for the class with name 'topic'.  The function 'topicName'
          returns the actual name used in this case. See the section on
          method documentation for the uses of 'type' to get help on
          formal methods.

_D_e_t_a_i_l_s:

     '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 '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) and 'dvips'. Depending on your
     'dvips' configuration, hardcopy will be sent to the printer or
     saved in a file.  If the programs are in non-standard locations
     and hence were not found at compile time, you can either set the
     options 'latexcmd' and 'dvipscmd', or the environment variables
     'R_LATEXCMD' and 'R_DVIPSCMD' appropriately. 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.

_M_e_t_h_o_d _D_o_c_u_m_e_n_t_a_t_i_o_n:

     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').

_N_o_t_e:

     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'.

_R_e_f_e_r_e_n_c_e_s:

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

_S_e_e _A_l_s_o:

     '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.

_E_x_a_m_p_l_e_s:

     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)

