Stacking data.frames in a list into a single data.frame, maintaining names(list) as an extra column

Question

I have a list of data frames which I would like to combine into a single data.frame. This is what my list looks like:

my_list <- list(
    m=data.frame(a = letters[1:5], b = 1:5, c = rnorm(5)), 
    n=data.frame(a = letters[1:5], b = 6:10, c = rnorm(5)))

> my_list
$m
  a b          c 
1 a 1  0.1151720  
2 b 2 -0.3785748  
3 c 3 -0.1446305  
4 d 4 -0.4300272  
5 e 5  1.1982312  

$n
  a  b          c 
1 a  6  1.2079439 
2 b  7 -1.2414251 
3 c  8  0.4362390 
4 d  9 -0.5844525 
5 e 10  0.1420070 

I'd like to stack these on top of each other, but without losing the context of the name of the data.frame ("m", "n"). Ideally, the name of the original data frame would be included as an extra column in the final data frame. One way would be to just add the extra column before using rbind.fill:

for(i in 1:length(my_list)) my_list[[i]][, 4] <- names(my_list)[i]
library(plyr)
rbind.fill(my_list)

   a  b          c V4
1  a  1  0.1151720  m
2  b  2 -0.3785748  m
3  c  3 -0.1446305  m
4  d  4 -0.4300272  m
5  e  5  1.1982312  m
6  a  6  1.2079439  n
7  b  7 -1.2414251  n
8  c  8  0.4362390  n
9  d  9 -0.5844525  n
10 e 10  0.1420070  n    

What I don't like about that is I have to take care about the dimensions of the data frame and the name of the extra column.

Isn't there a function out there that does that better, in a more flexible and generic way?

Answer 1

Another possibility:

library(plyr)
ldply(my_list)
#    .id a  b          c
# 1    m a  1 -0.1294107
# 2    m b  2  0.8867361
# 3    m c  3 -0.1513960
# 4    m d  4  0.3297912
# 5    m e  5 -3.2273228
# 6    n a  6 -0.7717918
# 7    n b  7  0.2865486
# 8    n c  8 -1.2205120
# 9    n d  9  0.4345504
# 10   n e 10  0.8001769