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  for a group generic is loaded, the methods defined become methods
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  for a group generic is loaded, the methods defined become methods
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  for the members of the group, but only if no method has been
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  for the members of the group, but only if no method has been
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  specified directly for the member function for the same signature.
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  specified directly for the member function for the same signature.
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  The effect is that group generic definitions are selected before
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  The effect is that group generic definitions are selected before
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  inherited methods but after directly specified methods.  For more on
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  inherited methods but after directly specified methods.  For more on
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  method selection, see \code{\link{Methods}}.
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  method selection, see \code{\link{Methods_Details}}.
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There are also
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There are also
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  S3 groups \code{Math}, \code{Ops}, \code{Summary} and
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  S3 groups \code{Math}, \code{Ops}, \code{Summary} and
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  \code{Complex}, see \code{?\link{S3groupGeneric}},
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  \code{Complex}, see \code{?\link{S3groupGeneric}},
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  with no corresponding \R objects, but these are irrelevant for S4
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  with no corresponding \R objects, but these are irrelevant for S4
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  All the functions in these groups (other than the group generics
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  All the functions in these groups (other than the group generics
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  themselves) are basic functions in \R.  They are not by default S4 generic
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  themselves) are basic functions in \R.  They are not by default S4 generic
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  functions, and many of them are defined as primitives.  However, you can still define
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  functions, and many of them are defined as primitives.  However, you can still define
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  formal methods for them, both individually and via the group generics.  It all works more or less as you
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  formal methods for them, both individually and via the group generics.  It all works more or less as you
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  might expect, admittedly via a bit of trickery in the background.
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  might expect, admittedly via a bit of trickery in the background.
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  See \link{Methods} for details.
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  See \link{Methods_Details} for details.
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  Note that two members of the \code{Math} group, \code{\link{log}} and
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  Note that two members of the \code{Math} group, \code{\link{log}} and
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  \code{\link{trunc}}, have \dots as an extra formal argument.
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  \code{\link{trunc}}, have \dots as an extra formal argument.
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  Since methods for \code{Math} will have only one formal argument,
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  Since methods for \code{Math} will have only one formal argument,
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  you must set a specific method for these functions in order to call
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  you must set a specific method for these functions in order to call
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  them with the extra argument(s).
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  them with the extra argument(s).
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  For further details about group generic functions see section 10.5 of
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  For further details about group generic functions see section 10.5 of
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  \emph{Software for Data Analysis}.
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  the second reference.
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}
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}
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\references{
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\references{
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 Chambers, John M. (2016)
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 \emph{Extending R},
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  Chapman & Hall.
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(Chapters 9 and 10.)
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 Chambers, John M. (2008)
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 Chambers, John M. (2008)
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 \emph{Software for Data Analysis: Programming with R}
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 \emph{Software for Data Analysis: Programming with R}
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  Springer.  (For the R version.)
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  Springer. (Section 10.5)
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 Chambers, John M. (1998)
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 \emph{Programming with Data}
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 Springer (For the original S4 version).
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}
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}
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\seealso{ The function \code{\link{callGeneric}} is nearly always
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\seealso{ The function \code{\link{callGeneric}} is nearly always
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  relevant when writing a method for a group generic.  See the
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  relevant when writing a method for a group generic.  See the
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  examples below and in section 10.5 of \emph{Software for Data Analysis}.
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  examples below and in section 10.5 of \emph{Software for Data Analysis}.
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