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