Group generic methods can be defined for four pre-specified groups of
functions, `Math`

, `Ops`

, `Summary`

and `Complex`

.
(There are no objects of these names in base R, but there are in the
methods package.)

A method defined for an individual member of the group takes precedence over a method defined for the group as a whole.

```
## S3 methods for group generics have prototypes:
````Math(x, \dots)`

`Ops(e1, e2)`

`Complex(z)`

`Summary(\dots, na.rm = FALSE)`

x, z, e1, e2

objects.

…

further arguments passed to methods.

na.rm

logical: should missing values be removed?

These functions are all primitive and internal generic.

The details of method dispatch and variables such as `.Generic`

are discussed in the help for `UseMethod`

. There are a
few small differences:

For the operators of group

`Ops`

, the object`.Method`

is a length-two character vector with elements the methods selected for the left and right arguments respectively. (If no method was selected, the corresponding element is`""`

.)Object

`.Group`

records the group used for dispatch (if a specific method is used this is`""`

).

There are four *groups* for which S3 methods can be written,
namely the `"Math"`

, `"Ops"`

, `"Summary"`

and
`"Complex"`

groups. These are not R objects in base R, but
methods can be supplied for them and base R contains
`factor`

, `data.frame`

and
`difftime`

methods for the first three groups. (There is
also a `ordered`

method for `Ops`

,
`POSIXt`

and `Date`

methods for `Math`

and `Ops`

, `package_version`

methods for `Ops`

and `Summary`

, as well as a `ts`

method for
`Ops`

in package stats.)

Group

`"Math"`

:`abs`

,`sign`

,`sqrt`

,`floor`

,`ceiling`

,`trunc`

,`round`

,`signif`

`exp`

,`log`

,`expm1`

,`log1p`

,`cos`

,`sin`

,`tan`

,`cospi`

,`sinpi`

,`tanpi`

,`acos`

,`asin`

,`atan`

`cosh`

,`sinh`

,`tanh`

,`acosh`

,`asinh`

,`atanh`

`lgamma`

,`gamma`

,`digamma`

,`trigamma`

`cumsum`

,`cumprod`

,`cummax`

,`cummin`

Members of this group dispatch on

`x`

. Most members accept only one argument, but members`log`

,`round`

and`signif`

accept one or two arguments, and`trunc`

accepts one or more.Group

`"Ops"`

:`"+"`

,`"-"`

,`"*"`

,`"/"`

,`"^"`

,`"%%"`

,`"%/%"`

`"&"`

,`"|"`

,`"!"`

`"=="`

,`"!="`

,`"<"`

,`"<="`

,`">="`

,`">"`

This group contains both binary and unary operators (

`+`

,`-`

and`!`

): when a unary operator is encountered the`Ops`

method is called with one argument and`e2`

is missing.The classes of both arguments are considered in dispatching any member of this group. For each argument its vector of classes is examined to see if there is a matching specific (preferred) or

`Ops`

method. If a method is found for just one argument or the same method is found for both, it is used. If different methods are found, there is a warning about ‘incompatible methods’: in that case or if no method is found for either argument the internal method is used.Note that the

`data.frame`

methods for the comparison (`"Compare"`

:`==`

,`<`

, …) and logic (`"Logic"`

:`&`

`|`

and`!`

) operators return a logical`matrix`

instead of a data frame, for convenience and back compatibility.If the members of this group are called as functions, any argument names are removed to ensure that positional matching is always used.

Group

`"Summary"`

:`all`

,`any`

`sum`

,`prod`

`min`

,`max`

`range`

Members of this group dispatch on the first argument supplied.

Group

`"Complex"`

:`Arg`

,`Conj`

,`Im`

,`Mod`

,`Re`

Members of this group dispatch on

`z`

.

Note that a method will be used for one of these groups or one of its
members *only* if it corresponds to a `"class"`

attribute,
as the internal code dispatches on `oldClass`

and not on
`class`

. This is for efficiency: having to dispatch on,
say, `Ops.integer`

would be too slow.

The number of arguments supplied for primitive members of the
`"Math"`

group generic methods is not checked prior to dispatch.

There is no lazy evaluation of arguments for group-generic functions.

Appendix A, *Classes and Methods* of
Chambers, J. M. and Hastie, T. J. eds (1992)
*Statistical Models in S.*
Wadsworth & Brooks/Cole.

`methods`

for methods of non-internal generic functions.

S4groupGeneric for group generics for S4 methods.

```
# NOT RUN {
require(utils)
d.fr <- data.frame(x = 1:9, y = stats::rnorm(9))
class(1 + d.fr) == "data.frame" ##-- add to d.f. ...
methods("Math")
methods("Ops")
methods("Summary")
methods("Complex") # none in base R
# }
```

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