[R] Converting a list to a data frame

[Charles Determan]

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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