R: Convert lists into data.frame or matrix

Question

mylist = list(list(c(1, 2, 3, 4, 5), c(2, 3, 9)), list(c(1, 4, 2, 1, 3), c(2, 4, 3)))
> mylist
[[1]]
[[1]][[1]]
[1] 1 2 3 4 5

[[1]][[2]]
[1] 2 3 9


[[2]]
[[2]][[1]]
[1] 1 4 2 1 3

[[2]][[2]]
[1] 2 4 3

I have a list (or lists within list) where the first element is a vector of 5 values, and the second element is a vector of 3 values. I would like my output to be something like

      [,1] [,2] [,3] [,4] [,5] 
 [1,]    1    2    3    4    5   
 [2,]    1    4    2    1    3

for the first element and

      [,1] [,2] [,3] 
 [1,]    2    3    9    
 [2,]    2    4    3   

for the second element.

I've tried using do.call(rbind, mylist) but that didn't seem to work since I have multiple elements. What's a way to convert this list to 2 data.frames or matrices?

Answer 1

Try this:

firstm<-sapply(X = mylist,"[[",1,simplify = T)
secondm<-sapply(X = mylist,"[[",2,simplify = T)

This will give you two matrices, when you provide the simplify = T argument. To get the desired format you can use the transpose using t() .

#> firstm

#       [,1] [,2]
#[1,]     1    1
#[2,]     2    4
#[3,]     3    2
#[4,]     4    1
#[5,]     5    3

 firstm<-t(firstm)
#> firstm 

#    [,1] [,2] [,3] [,4] [,5]
#[1,]    1    2    3    4    5
#[2,]    1    4    2    1    3

Answer 2

So close with your do.call . Make it call Map over your list objects, with rbind as the function:

do.call(Map, c(rbind, mylist))
#[[1]]
#     [,1] [,2] [,3] [,4] [,5]
#[1,]    1    2    3    4    5
#[2,]    1    4    2    1    3

#[[2]]
#     [,1] [,2] [,3]
#[1,]    2    3    9
#[2,]    2    4    3

Answer 3

Here is an option using tidyverse

library(tidyverse)
mylist %>%
     transpose %>%
     map(unlist) %>%
     map(matrix, nrow=2, byrow = TRUE)
#[[1]]
#     [,1] [,2] [,3] [,4] [,5]
#[1,]    1    2    3    4    5
#[2,]    1    4    2    1    3

#[[2]]
#      [,1] [,2] [,3]
#[1,]    2    3    9
#[2,]    2    4    3

Answer 4

Another way could be to strip the hierarchy from the list with the flatten function in purrr . So,

y <- flatten(mylist)
do.call(rbind, y[c(1,3)])
do.call(rbind, y[c(2,4)])

Output:

  > do.call(rbind, y[c(1,3)])
      [,1] [,2] [,3] [,4] [,5]
[1,]    1    2    3    4    5
[2,]    1    4    2    1    3

> do.call(rbind, y[c(2,4)])
     [,1] [,2] [,3]
[1,]    2    3    9
[2,]    2    4    3