Writing Methods for Classes Contained in Another Class
Let's say I have a structure that looks like this:
obj <- list()
obj$title <- "Hello"
obj$data <- data.frame(c(1,2,3,4,5),c(5,4,3,2,1))
class(obj) <- "myclass"
I know I can write methods in the class:
myfunction <- function(obj,...) {
UseMethod("myfunction")
}
myfunction.myclass <- function(obj,...) {
# magic
}
But how would I write a method for the data contained in the object based on their class. I mean without having to write everything in one function. Kind of like ...
myfunction.myclass.data.frame <- function(obj,...) {
# do something if class(obj$data) == "data.frame"
}
myfunction.myclass.character <- function(obj,...) {
# do something if class(obj$data) == "character"
}
myfunction.myclass.numeric <- function(obj,...) {
# do something if class(obj$data) == "numeric"
}
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What you can do is make it a myfunction.myclass()
generic second level (where myfunction()
would be the first level generator) by calling UseMethod()
from it, and instead of omitting the second argument (which is usually the default for the first argument of the include function), you can pass it obj$data
... This will send a named function based on the class obj$data
:
## define first-level obj generic
myfunction <- function(obj,...) UseMethod('myfunction');
## define second-level obj$data generic
myfunction.myclass <- function(obj,...) UseMethod('myfunction.myclass',obj$data);
## define obj$data specifics
myfunction.myclass.data.frame <- function(obj,...) { cat('----- class -----\ndata.frame\n----- obj -----\n'); print(obj); cat('----- args -----\n'); print(list(...)); };
myfunction.myclass.character <- function(obj,...) { cat('----- class -----\ncharacter\n----- obj -----\n'); print(obj); cat('----- args -----\n'); print(list(...)); };
myfunction.myclass.numeric <- function(obj,...) { cat('----- class -----\nnumeric\n----- obj -----\n'); print(obj); cat('----- args -----\n'); print(list(...)); };
myfunction.myclass.default <- function(obj,...) { cat('----- class -----\ndefault\n----- obj -----\n'); print(obj); cat('----- args -----\n'); print(list(...)); };
## create test obj
obj <- list();
obj$title <- 'Hello';
class(obj) <- 'myclass';
## demo 1: data.frame
obj$data <- data.frame(a=c(1,2,3,4,5),b=c(5,4,3,2,1));
myfunction(obj,1,'a',T);
## ----- class -----
## data.frame
## ----- obj -----
## $title
## [1] "Hello"
##
## $data
## a b
## 1 1 5
## 2 2 4
## 3 3 3
## 4 4 2
## 5 5 1
##
## attr(,"class")
## [1] "myclass"
## ----- args -----
## [[1]]
## [1] 1
##
## [[2]]
## [1] "a"
##
## [[3]]
## [1] TRUE
## demo 2: character
obj$data <- letters;
myfunction(obj,2,'b',F);
## ----- class -----
## character
## ----- obj -----
## $title
## [1] "Hello"
##
## $data
## [1] "a" "b" "c" "d" "e" "f" "g" "h" "i" "j" "k" "l" "m" "n" "o" "p" "q" "r" "s" "t" "u" "v" "w" "x" "y" "z"
##
## attr(,"class")
## [1] "myclass"
## ----- args -----
## [[1]]
## [1] 2
##
## [[2]]
## [1] "b"
##
## [[3]]
## [1] FALSE
## demo 3: numeric
obj$data <- 1:10;
myfunction(obj,3,'c',T);
## ----- class -----
## numeric
## ----- obj -----
## $title
## [1] "Hello"
##
## $data
## [1] 1 2 3 4 5 6 7 8 9 10
##
## attr(,"class")
## [1] "myclass"
## ----- args -----
## [[1]]
## [1] 3
##
## [[2]]
## [1] "c"
##
## [[3]]
## [1] TRUE
## demo 4: default (logical)
obj$data <- T;
myfunction(obj,4,'d',F);
## ----- class -----
## default
## ----- obj -----
## $title
## [1] "Hello"
##
## $data
## [1] TRUE
##
## attr(,"class")
## [1] "myclass"
## ----- args -----
## [[1]]
## [1] 4
##
## [[2]]
## [1] "d"
##
## [[3]]
## [1] FALSE
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