[R] Data.frames can not hold objects...What can be done in the following scenario?

[Rui Barradas]

Hello,

What you need is to have your function return a list, not a vector. Like 
this

testfun <- function (x, y) list(seq(x, y, 1))

testframe<-data.frame(xvalues=c(2,3),yvalues=c(4,5))

testframe$newcolumn <- apply(testframe, 1, function(x) testfun(x[1], x[2]))
class(testframe$newcolumn)  # [1] "list"

Then you access lists and list elements.

testframe$newcolumn[[1]]  # a list with just one element
testframe$newcolumn[[1]][[1]]  # that element, a vector
testframe$newcolumn[[1]][[1]][2]  # the vector's 2nd element


Since you want the function to return vectors in order to do further 
computations, you'll access those vectors by varying the list index,


testframe$newcolumn[[1]][[1]]  # first list, it's only vector
testframe$newcolumn[[2]][[1]]  # second list, it's only vector


Etc.

Hope this helps,

Rui Barradas

Em 10-06-2012 12:29, Onur Uncu escreveu:
> Thank you Duncan. A follow-up question is, how can I achieve the
> desired result in the earlier email? (i.e. Add the resulting vectors
> as a new column to the existing data.frame?)   I tried the following:
>
> testframe$newcolumn<-apply(testframe,1,function(x)testfun(x[1],x[2]))
>
> but I am getting the following error:
>
> Error in `$<-.data.frame`(`*tmp*`, "vecss", value = c(2, 3, 4, 3, 4, 5
> : replacement has 3 rows, data has 2
>
> Thanks for the help.
>
>
> On Sun, Jun 10, 2012 at 12:02 PM, Duncan Murdoch
> <murdoch.duncan at gmail.com> wrote:
>> On 12-06-10 6:41 AM, Onur Uncu wrote:
>>>
>>> R-Help community,
>>>
>>> I understand that data.frames can hold elements of type double, string
>>> etc but NOT objects (such as a matrix etc).
>>
>>
>> That is incorrect.  Dataframes can hold list vectors.  For example:
>>
>> A <- data.frame(x = 1:3)
>> A$y <- list(matrix(1, 2,2), matrix(2, 3,3), matrix(3,4,4))
>>
>> A[1,2] will now extract the 2x2 matrix, A[2,2] will extract the 3x3, etc.
>>
>> Duncan Murdoch
>>
>> This is not convenient for
>>>
>>> me in the following situation. I have a function that takes 2 inputs
>>> and returns a vector:
>>>
>>> testfun<- function (x,y) seq(x,y,1)
>>>
>>> I have a data.frame defined as follows:
>>>
>>> testframe<-data.frame(xvalues=c(2,3),yvalues=c(4,5))
>>>
>>> I would like to apply testfun to every row of testframe and then
>>> create a new column in the data.frame which holds the returned vectors
>>> as objects. Why do I want this? Because the returned vectors are an
>>> intermediate step towards further calculations. It would be great to
>>> keep adding new columns to the data.frame with the intermediate
>>> objects. But this is not possible since data.frames can not hold
>>> objects as elements. What do you suggest as an elegant solution in
>>> this scenario? Thank you for any help!
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>> I would love to hear if forum
>>>
>>> ______________________________________________
>>> R-help at r-project.org mailing list
>>> https://stat.ethz.ch/mailman/listinfo/r-help
>>> PLEASE do read the posting guide
>>> http://www.R-project.org/posting-guide.html
>>> and provide commented, minimal, self-contained, reproducible code.
>>
>>
>
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>