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This page collects some S4 examples.
More details about this topic can be found on
<a href="https://github.com/hadley/devtools/wiki/" target="_blank">
Hadley's Wiki pages</a>
including
<a href="https://github.com/hadley/devtools/wiki/S3" target="_blank">S3</a>,
<a href="https://github.com/hadley/devtools/wiki/S4" target="_blank">S4</a>,
and
<a href="https://github.com/hadley/devtools/wiki/R5" target="_blank">R5</a>
systems.
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#### <b>Examples:</b><br>
- <font color="#800000"><b>S4 Class and Method</b></font>
This is a quick example to use S4 class and method to extend functions
where all <code>foo.*</code> need to have the same number of arguments.
S4 signature will determine the input type and call the corresponding
function.
```
rm(list = ls(all.names = TRUE))
foo.default <- function(x, y, z) cat("call foo.default\n")
foo.double <- function(x, y, z) cat("call foo.double\n")
foo.myobj <- function(x, y = NULL, z = NULL) cat("call foo.myobj\n")
setClass("myobj", representation(x = "numeric"))
setGeneric(name = "foo", useAsDefault = foo.default)
setMethod(f = "foo",
signature = signature(x = "myobj"),
definition = foo.myobj)
setMethod(f = "foo",
signature = signature(x = "numeric", y = "numeric", z = "numeric"),
definition = foo.double)
a <- new("myobj")
foo(a)
foo(1)
foo(1, 2, 3)
```
- <font color="#800000"><b>More S4 Methods</b></font>
This is a silly example, but somehow useful in some cases with
different number and different type of input arguments.
```
rm(list = ls(all.names = TRUE))
foo.default <- function(x, dim, bldim, ctxt){
if(!missing(ctxt)){
stop("Input is incorrect.")
} else{
foo.2(NULL, x, dim, bldim)
}
cat("cat foo.default\n")
}
foo.1 <- function(x, dim = NULL, bldim = NULL, ctxt = NULL){
cat("call foo.1\n")
}
foo.2 <- function(x = NULL, dim, bldim, ctxt){
cat("call foo.2\n")
}
foo.3 <- function(x, dim = NULL, bldim = NULL, ctxt = NULL){
cat("call foo.3\n")
}
setClass("myobj", representation(x = "numeric"))
setGeneric(name = "ownany", useAsDefault = foo.default)
setMethod(f = "ownany",
signature = signature(x = "myobj"),
definition = foo.1)
setMethod(f = "ownany",
signature = signature(dim = "numeric", bldim = "numeric", ctxt = "numeric"),
definition = foo.2)
setMethod(f = "ownany",
signature = signature(x = "numeric", dim = "missing", bldim = "missing", ctxt = "missing"),
definition = foo.3)
a <- new("myobj")
ownany(a)
ownany(dim = 1, bldim = 2, ctxt = 3)
ownany(1)
ownany(1, 2, 3)
```
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