Converting a list to a data frame

David L Carlson <dcarlson at tamu.edu>
    on Wed, 2 May 2018 21:43:52 +0000 writes:
Typo: dat[[z]] should be x[[z]]:

x2 <- do.call(rbind, lapply(names(x), function(z) 
                            data.frame(type=z, x[[z]])))
x2
  type x y
1    A 1 3
2    A 2 4
3    B 5 7
4    B 6 8

David C
Before this thread gets carried away to data.table and
tibbleverse (and as nobody else has done so) :

Let me nominate this beautiful solution by
Bill Dunlap and David Carlson to win the prize  with a 10 out 10 grade:

Beautiful use of  do.call() and lapply(), two of the most
versatile and important functions from the base R toolbox.

Congratulations!

Martin Maechler
R Core Team
-----Original Message-----
From: R-help <r-help-bounces at r-project.org> On Behalf Of David L Carlson
Sent: Wednesday, May 2, 2018 3:51 PM
To: William Dunlap <wdunlap at tibco.com>; Kevin E. Thorpe <kevin.thorpe at utoronto.ca>
Cc: r-help mailing list <r-help at r-project.org>
Subject: Re: [R] Converting a list to a data frame

Or add the type column first and then rbind:

x <- list(A=data.frame(x=1:2, y=3:4),B=data.frame(x=5:6,y=7:8))
x2 <- do.call(rbind, lapply(names(x), function(z) 
      data.frame(type=z, dat[[z]])))

----------------------------------------
David L Carlson
Department of Anthropology
Texas A&M University
College Station, TX 77843-4352

-----Original Message-----
From: R-help <r-help-bounces at r-project.org> On Behalf Of William Dunlap via R-help
Sent: Wednesday, May 2, 2018 12:28 PM
To: Kevin E. Thorpe <kevin.thorpe at utoronto.ca>
Cc: R Help Mailing List <r-help at r-project.org>
Subject: Re: [R] Converting a list to a data frame

x1 <- do.call(rbind, c(x, list(make.row.names=FALSE)))
x2 <- cbind(type=rep(names(x), vapply(x, nrow, 0)), x1)
str(x2)
'data.frame':   4 obs. of  3 variables:
 $ type: Factor w/ 2 levels "A","B": 1 1 2 2
 $ x   : int  1 2 5 6
 $ y   : int  3 4 7 8

Bill Dunlap
TIBCO Software
wdunlap tibco.com

On Wed, May 2, 2018 at 10:11 AM, Kevin E. Thorpe <kevin.thorpe at utoronto.ca>
wrote:

I suspect this is pretty easy, but I'm having trouble figuring it out.
Basically, I have a list of data frames such as the following example:

list(A=data.frame(x=1:2, y=3:4),B=data.frame(x=5:6,y=7:8))

I would like to turn this into  data frame where the list elements are 
essentially rbind'ed together and the element name becomes a new variable.
For example, I would like to turn the list above into a data frame 
that looks like this:

data.frame(type=c("A","A","B","B"),x=c(1:2,5:6),y=c(3:4,7:8))

Appreciate any pointers.

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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Converting a list to a data frame

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