On 07/18/2013 03:47 AM, Simon Zehnder wrote:
Hi Christopher,
I think, that "save" is no generic function like "plot", "show", etc. So at
first you have to determine a generic.
setGeneric("save", function(x, file_Path) standardGeneric("save"))
The implementation offered by Christofer shows write.table, and the end result
is a text file rather than a binary file expected from base::save. This makes it
seem inappropriate to use 'save' in this context.
Instead, it seems that what Cristofer wants to implement is functionality to
support write.table. ?write.table says
'write.table' prints its required argument 'x' (after converting
it to a data frame if it is not one nor a matrix)
So implementing an S3 method
as.data.frame.MyClass <-
function(x, row.names=NULL, optional=FALSE, ...)
{
x@x
}
is all that is needed, gaining lots of flexibility by re-using the code of
write.table.
myClass = new("MyClass", x=data.frame(x=1:3, y=3:1))
write.table(myClass, stdout())
In the case of a 'save' method producing binary output (but this is what save
does already...), I think it's better practice to promote the non-generic 'save'
to an S4 generic using it's existing arguments; in this case it makes sense to
restrict dispatch to '...', so
setGeneric("save", signature="...")
The resulting generic is
> getGeneric("save")
standardGeneric for "save" defined from package ".GlobalEnv"
function (..., list = character(), file = stop("'file' must be specified"),
ascii = FALSE, version = NULL, envir = parent.frame(), compress = !ascii,
compression_level, eval.promises = TRUE, precheck = TRUE)
standardGeneric("save")
<environment: 0x4a7b860>
Methods may be defined for arguments: ...
Use showMethods("save") for currently available ones.
This means that a method might be defined as
setMethod("save", "MyClass", function(..., list = character(),
file = stop("'file' must be specified"), ascii = FALSE, version = NULL,
envir = parent.frame(), compress = !ascii, compression_level,
eval.promises = TRUE, precheck = TRUE)
{
## check non-sensical or unsupported user input for 'MyClass'
if (!is.null(version))
stop("non-NULL 'version' not supported for 'MyClass'")
## ...
## implement save on MyClass
})
It might be that Christofer wants to implement a 'write.table-like' (text
output) or a 'save-like' (binary output) function that really does not conform
to the behavior of write.table (e.g., producing output that could not be input
by read.table) or save. Then I think the better approach is to implement
writeMyClass (for text output) or saveMyClass (for binary output).
Martin
Now your definition via setMethod.
Best
Simon
On Jul 18, 2013, at 12:09 PM, Christofer Bogaso <bogaso.christo...@gmail.com>
wrote:
Hello again,
I am trying to define the 'save' method for my S4 class as below:
setClass("MyClass", representation(
Slot1 = "data.frame"
))
setMethod("save", "MyClass", definition = function(x, file_Path) {
write.table(x@Slot1, file = file_Path, append = FALSE, quote =
TRUE,
sep = ",",
eol = "\n", na = "NA", dec =
".", row.names = FALSE,
col.names = TRUE, qmethod = c("escape",
"double"),
fileEncoding = "")
})
However while doing this I am getting following error:
Error in conformMethod(signature, mnames, fnames, f, fdef, definition) :
in method for ‘save’ with signature ‘list="MyClass"’: formal
arguments (list = "MyClass", file = "MyClass", ascii = "MyClass",
version = "MyClass", envir = "MyClass", compress = "MyClass",
compression_level = "MyClass", eval.promises = "MyClass", precheck =
"MyClass") omitted in the method definition cannot be in the signature
Can somebody point me what will be the correct approach to define
'save' method for S4 class?
Thanks and regards,
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