[datatable-help] Discrepancy between as.data.frame & as.data.table when handling nested lists

[Ricardo Saporta]

Hey Frank,

Thanks for pointing out that SO link, I had missed it.

All,

I'm curious as to which used cases this functionality would be used in
(used for?)

thanks,
Rick



On Wed, Aug 7, 2013 at 8:14 PM, Frank Erickson <FErickson at psu.edu> wrote:

> Hi Rick,
>
> I guess it's intentional: Matthew saw this SO question (since he edited
> one of the answers):
> http://stackoverflow.com/questions/9547518/creating-a-data-frame-where-a-column-is-a-list
>
> Some musings: Of course, to reproduce as.data.frame-like behavior, you can
> un-nest the list, so both functions treat it the same way.
>
> Z <- unlist(Y,recursive=FALSE)
>
> identical(as.data.table(Z),as.data.table(as.data.frame(Z))) # TRUE
> # or, equivalently (?)
> identical(do.call(data.table,Z),data.table(do.call(data.frame,Z))) # TRUE
>
>
> On the other hand, going back the other direction (getting data.table-like
> behavior when data.frame's is the default) is more awkward, as seen in that
> SO question (where they mention protecting each sublist with the I()
> function). Besides, I'm with @flodel, who asked the SO question, in
> expecting data.table's behavior: one top-level item in the list mapping to
> one column in the result...
>
> --Frank
>
> On Wed, Aug 7, 2013 at 4:56 PM, Ricardo Saporta <
> saporta at scarletmail.rutgers.edu> wrote:
>
>> Hi all,
>>
>> Note the following discrepancy in structure between as.data.frame &
>> as.data.table when called on a nested list.
>> as.data.frame converts the sublist into individual columns whereas
>> as.data.table stacks them into a single column and creates additional rows.
>>
>> Is this intentional?
>> -Rick
>>
>>
>> as.data.frame(X)
>> #        start       type      end data.editDist data.second
>> # 1 start_node is_similar end_node             1  HelloWorld
>>
>> as.data.table(X)
>> #         start       type      end       data
>> # 1: start_node is_similar end_node          1
>> # 2: start_node is_similar end_node HelloWorld
>>
>>
>>
>>
>> ### Copy+Paste'able Below ###
>>
>> # Example 1:
>> X <-  structure(list(start = "start_node", type = "is_similar", end =
>> "end_node",
>>     data = structure(list(editDist = 1, second = "HelloWorld"), .Names =
>> c("editDist",
>>     "second"))), .Names = c("start", "type", "end", "data"))
>>
>> as.data.frame(X)
>> as.data.table(X)
>>
>> as.data.table(as.data.frame(X))
>>
>>
>> # Example 2, with more elements:
>> Y <- structure(list(start = c("start_node", "start_node"), type =
>> c("is_similar", "is_similar"), end = c("end_node", "end_node"), data =
>> structure(list(editDist = c(1, 1), second = c("HelloWorld", "HelloWorld")),
>> .Names = c("editDist", "second"))), .Names = c("start", "type", "end",
>> "data"))
>>
>> as.data.frame(Y)
>> as.data.table(Y)
>>
>>
>> _______________________________________________
>> datatable-help mailing list
>> datatable-help at lists.r-forge.r-project.org
>>
>> https://lists.r-forge.r-project.org/cgi-bin/mailman/listinfo/datatable-help
>>
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.r-forge.r-project.org/pipermail/datatable-help/attachments/20130807/185c9b29/attachment-0001.html>