Short answer: there is a default method used here which returns a matrix. It's
defined at the C-level for speed so you don't see it with methods()
Longer: cbind() isn't a regular S3 generic since it has no UseMethod(). Look at
WRE and R-Internals (internal generics) for more info.
Best (and good question!),
Michael
On Jul 9, 2012, at 10:21 PM, James Long <jpl2...@gmail.com> wrote:
> ## Hi, I'm having trouble understanding how the cbind function decides what
> method to apply to its arguments. Easy cut and paste code below.
>
>>
>
>>
>
>>
>
>> ## create two columns
>
>> c1 <- c("A","A","B","B")
>
>> c2 <- 1:4
>
>>
>
>> ## cbind outputs a matrix with elements that are characters, seems
> reasonable
>
>> out <- cbind(c1,c2)
>
>> out
>
> c1 c2
>
> [1,] "A" "1"
>
> [2,] "A" "2"
>
> [3,] "B" "3"
>
> [4,] "B" "4"
>
>> class(out)
>
> [1] "matrix"
>
>> mode(out)
>
> [1] "character"
>
>>
>
>>
>
>> ## there are two methods associated with cbind. so i assume that
>
>> ## cbind is calling the data.frame method, because neither of my
>
>> ## arguments are of ts class
>
>> methods(cbind)
>
> [1] cbind.data.frame cbind.ts*
>
>
> Non-visible functions are asterisked
>
>>
>
>>
>
>> ## now i explicitly tell cbind to use the data.frame method
>
>> ## (which is what i assumed it was doing automatically in the last
> example)
>
>> ## but this produces something very different from before, a data.frame
>
>> out2 <- cbind.data.frame(c1,c2)
>
>> out2
>
> c1 c2
>
> 1 A 1
>
> 2 A 2
>
> 3 B 3
>
> 4 B 4
>
>> class(out2)
>
> [1] "data.frame"
>
>> mode(out2)
>
> [1] "list"
>
>>
>
>>
>
>> ## can someone explain why these outputs are different. Thanks, James.
>
>>
>
>
>
>
>
>
>
> c1 <- c("A","A","B","B")
>
> c2 <- 1:4
>
> out <- cbind(c1,c2)
>
> out
>
> class(out)
>
> mode(out)
>
> methods(cbind)
>
> out2 <- cbind.data.frame(c1,c2)
>
> out2
>
> class(out2)
>
> mode(out2)
>
> [[alternative HTML version deleted]]
>
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