Converting the names of a list elements as a variable in a data.frame

I have a named List of data.frames. I was wondering how to convert the name ("bar1",…,"bar4") of each element List as a column next to each data.frame?

My final desired_output is shown below.

List <- list(bar1=data.frame(study="A",sd = 1), bar2=data.frame(study=c("B","C"),sd=2:3),
     bar3=data.frame(study="Z",sd = 4), bar4=data.frame(study="H",sd=5))

# desired_output:
"
  study sd   id
      A  1 bar1
      B  2 bar2
      C  3 bar2
      Z  4 bar3
      H  5 bar4
"

>Solution :

Here’s a tidyverse solution using map2() from the purrr library. First, I grabbed the names of the list elements and stored them in a vector, n:

n <- names(List)

Then we can iterate over List and n at the same time, calling cbind() to add a variable (i.e., column) to each data frame:

map2(List, n, ~ cbind(.x, Name = .y))

Output:

$bar1

  study sd Name

1     A  1 bar1

$bar2

  study sd Name

1     B  2 bar2

2     C  3 bar2
$bar3

  study sd Name

1     Z  4 bar3
$bar4

  study sd Name

1     H  5 bar4

We can collapse List to a single data frame with a call to bind_rows():

result <- map2(List, n, ~ cbind(.x, Name = .y))
bind_rows(result)

Output:

  study sd Name

1     A  1 bar1

2     B  2 bar2

3     C  3 bar2

4     Z  4 bar3

5     H  5 bar4

In one statement:

map2(List, names(List), ~ cbind(.x, Name = .y)) %>% 
  bind_rows()