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\details{
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\details{
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An \R \dQuote{object} is a data object which has a \code{class} attribute.
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An \R \dQuote{object} is a data object which has a \code{class} attribute.
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A class attribute is a character vector giving the names of
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A class attribute is a character vector giving the names of
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the classes which the object \dQuote{inherits} from.
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the classes which the object \dQuote{inherits} from.
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If the object does not have a class attribute, it has an implicit
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If the object does not have a class attribute, it has an implicit
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class, \code{"matrix"}, \code{"array"} or the result of
|
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class. Matrices and arrays have class \code{"matrix"}
|
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or\code{"array"} followed by the class of the underlying vector.
|
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\code{\link{mode}(x)}.
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31 |
Most vectors have class the result of \code{\link{mode}(x)}, expect
|
| - |
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32 |
that integer vectors have class \code{c("integer", "numeric")} and
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33 |
real vectors have class \code{c("double", "numeric")}.
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34 |
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When a generic
|
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function \code{fun} is applied to an object with class attribute
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35 |
When a generic function \code{fun} is applied to an object with class
|
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\code{c("first", "second")}, the system searches for a function called
|
36 |
attribute \code{c("first", "second")}, the system searches for a
|
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\code{fun.first} and, if it finds it, applied it to the object. If no
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function called \code{fun.first} and, if it finds it, applied it to
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such function is found a function called \code{fun.second} is tried.
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the object. If no such function is found a function called
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If no class name produces a suitable function, the function
|
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\code{fun.second} is tried. If no class name produces a suitable
|
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function, the function \code{fun.default} is used, if it exists, or an
|
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\code{fun.default} is used.
|
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error results.
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42 |
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43 |
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Function \code{\link{methods}} can be used to find out about the
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Function \code{\link{methods}} can be used to find out about the
|
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methods for a particular generic function or class.
|
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methods for a particular generic function or class.
|
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46 |
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Now for some obscure details that need to appear somewhere. These
|
47 |
Now for some obscure details that need to appear somewhere. These
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statements after the call to \code{UseMethod} will not be evaluated as
|
52 |
statements after the call to \code{UseMethod} will not be evaluated as
|
| 49 |
\code{UseMethod} does not return. \code{UseMethod} can be called with
|
53 |
\code{UseMethod} does not return. \code{UseMethod} can be called with
|
| 50 |
more than two arguments: a warning will be given and additional
|
54 |
more than two arguments: a warning will be given and additional
|
| 51 |
arguments ignored. (They are not completely ignored in S.) If it is
|
55 |
arguments ignored. (They are not completely ignored in S.) If it is
|
| 52 |
called with just one argument, the class of the first argument of the
|
56 |
called with just one argument, the class of the first argument of the
|
| 53 |
enclosing function is used as \code{object}: unlike S this is the
|
57 |
enclosing function is used as \code{object}: unlike S this is the first
|
| 54 |
actual argument passed and not the current value of the object of that
|
58 |
actual argument passed and not the current value of the object of that
|
| 55 |
name.
|
59 |
name.
|
| 56 |
|
60 |
|
| 57 |
\code{NextMethod} invokes the next method (determined by the
|
61 |
\code{NextMethod} invokes the next method (determined by the
|
| 58 |
class). It does this by creating a special call frame for that
|
62 |
class). It does this by creating a special call frame for that
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| 76 |
environment in which the generic is defined (typically a name space).
|
80 |
environment in which the generic is defined (typically a name space).
|
| 77 |
So methods for a generic function need to either be available in the
|
81 |
So methods for a generic function need to either be available in the
|
| 78 |
environment of the call to the generic, or they must be registered.
|
82 |
environment of the call to the generic, or they must be registered.
|
| 79 |
It does not matter whether they are visible in the environment in
|
83 |
It does not matter whether they are visible in the environment in
|
| 80 |
which the generic is defined.
|
84 |
which the generic is defined.
|
| 81 |
|
- |
|
| 82 |
}
|
85 |
}
|
| 83 |
\note{
|
86 |
\note{
|
| 84 |
This scheme is called \emph{S3} (S version 3). For new projects,
|
87 |
This scheme is called \emph{S3} (S version 3). For new projects,
|
| 85 |
it is recommended to use the more flexible and robust \emph{S4} scheme
|
88 |
it is recommended to use the more flexible and robust \emph{S4} scheme
|
| 86 |
provided in the \pkg{methods} package.
|
89 |
provided in the \pkg{methods} package.
|
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