rbind dataframes from a list

问题:

One of my functions return a list of dataframes which I need to concatenate into 1 single dataframe. I do this using:

 do.call(rbind,list_df)

This used to work as expected. But for some strange reason (which is driving me nuts!) it no longer does. Now, instead of combining into a single df, it just retains it as separate lists. When I print the output this is what I get (the list had 2 dataframes with 5 columns each, and the output is retained as such without concatenation)

 out_df 
[1,] List,5
[2,] List,5

Even when i try this manually without do.call (as shown below) it still gives me the same output, without concatenation:

rbind(list_df[[1]],list_df[[2]])

I am at a loss trying to figure out what's happening. (Each dataframe in the list has the same attributes - similiar no. of columns and same names, so rbind'ing should ideally work)

回答1:

From the output of "out_df", it looks like a nested list. We could try

out <- do.call(rbind, do.call(c, list_df))
str(out)
# 'data.frame':   10 obs. of  5 variables:
# $ v1: int  1 2 3 4 5 1 2 3 4 5
# $ v2: int  6 7 8 9 10 6 7 8 9 10
# $ v3: int  11 12 13 14 15 11 12 13 14 15
# $ v4: int  16 17 18 19 20 16 17 18 19 20
# $ v5: int  21 22 23 24 25 21 22 23 24 25

data

list_df <- lapply(1:2, function(i) list(data.frame(v1=1:5, 
       v2= 6:10, v3= 11:15, v4 = 16:20, v5= 21:25)))

Using the OP's code,

do.call(rbind, list_df)
#     [,1]  
#[1,] List,5
#[2,] List,5