How to set the value of a slot(S4) using <- in R

Question

I have an object ob of class markovchain.

> ob
An object of class "markovchain"
Slot "states":
[1] "a" "b" "c" "d" "e"

Slot "byrow":
[1] TRUE

Slot "transitionMatrix":
   a  b  c  d  e
a  1  2  3  4  5
b  6  7  8  9 10
c 11 12 13 14 15
d 16 17 18 19 20
e 21 22 23 24 25

Slot "name":
[1] "deepak"

My task is to create a method to get and set the data of name slot.

Below is the method to get the data in the name slot.

> setGeneric("name", function(object) standardGeneric("name"))
[1] "name"
> setMethod("name", "markovchain", 
+           function(object) {
+             out <- object@name
+             return(out)
+           }
+ )
[1] "name"

It is working properly. See

> name(ob)
[1] "deepak"

Now my task is to set the data in the name slot. I have tried this

setGeneric("name<-", function(object, ob_name) standardGeneric("name<-"))
setMethod("name<-", "markovchain", 
          function(object, ob_name) {
            object@name <- ob_name
            object
          }
)

While setting the name I am getting an error.

> name(ob) <- "apple"
Error in `name<-`(`*tmp*`, value = "apple") : 
  unused argument (value = "apple")

I am not getting what I am doing wrong? Any help.

Answer 1

The problem is solved. Name of the last argument of the function must be value.

setGeneric("name", function(object) standardGeneric("name"))
setMethod("name", "markovchain", function(object) {
  out <- object@name
  return(out)
})

setGeneric("name<-", function(object, value) standardGeneric("name<-"))
setMethod("name<-", "markovchain", 
          function(object, value) {
            object@name <- value
            object
          }
)

See the output.

> name(ob)
[1] "deepak"
> name(ob) <- "value is changed"
> name(ob)
[1] "value is changed"