[R] Converting a list to a data frame

[Bert Gunter]

I believe that a slightly more efficient way of doing this without
leaving base R is:

cbind(do.call(rbind,x), set = rep(seq_along(x), vapply(x,nrow,1)) )


Cheers,
Bert


Bert Gunter

"The trouble with having an open mind is that people keep coming along
and sticking things into it."
-- Opus (aka Berkeley Breathed in his "Bloom County" comic strip )


On Fri, Nov 4, 2016 at 5:50 AM, Charles Determan <cdetermanjr at gmail.com> wrote:
> Hi Kevin,
>
> There may be a more elegant way but the following do.call and lapply should
> solve your problem.
>
> do.call(rbind, lapply(seq(length(x)), function(i) data.frame(set=i,
> x[[i]])))
>
> Regards,
> Charles
>
> On Fri, Nov 4, 2016 at 7:37 AM, Kevin E. Thorpe <kevin.thorpe at utoronto.ca>
> wrote:
>
>> There is probably a very simple elegant way to do this, but I have been
>> unable to find it. Here is a toy example. Suppose I have a list of data
>> frames like this.
>>
>>  print(x <- list('1'=data.frame(id=1:4,expand.grid(x1=0:1,x2=0:1)),'2'=
>> data.frame(id=5:8,expand.grid(x1=2:3,x2=2:3))))
>> $`1`
>>   id x1 x2
>> 1  1  0  0
>> 2  2  1  0
>> 3  3  0  1
>> 4  4  1  1
>>
>> $`2`
>>   id x1 x2
>> 1  5  2  2
>> 2  6  3  2
>> 3  7  2  3
>> 4  8  3  3
>>
>> The real application will have more than 2 elements so I'm looking for a
>> general approach. I basically want to rbind the data frames in each list
>> element and add a variable that adds the element name. In this example the
>> result would look something like this.
>>
>> rbind(data.frame(set='1',x[[1]]),data.frame(set='2',x[[2]]))
>>   set id x1 x2
>> 1   1  1  0  0
>> 2   1  2  1  0
>> 3   1  3  0  1
>> 4   1  4  1  1
>> 5   2  5  2  2
>> 6   2  6  3  2
>> 7   2  7  2  3
>> 8   2  8  3  3
>>
>> Obviously, for 2 elements the simple rbind works but I would like a
>> general solution for arbitrary length lists. Hopefully that is clear.
>>
>> Kevin
>>
>> --
>> Kevin E. Thorpe
>> Head of Biostatistics,  Applied Health Research Centre (AHRC)
>> Li Ka Shing Knowledge Institute of St. Michael's Hospital
>> Assistant Professor, Dalla Lana School of Public Health
>> University of Toronto
>> email: kevin.thorpe at utoronto.ca  Tel: 416.864.5776  Fax: 416.864.3016
>>
>> ______________________________________________
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>>
>
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>
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