Nested list to dataframe [using purrr + map]

问题

I've looked at a lot of posts so I'm sorry if this is redundant, but was hoping to get some help flattening a nested list:

test <- list()
test <- c(
  list("A" = c(list("1"), list("2"), list("3"))), 
  list("B" = c(list("4"), list("5"), list("6")))
)

Desired Output

  name subcat
1    A      1
2    A      2
3    A      3
4    B      4
5    B      5
6    B      6

I'm struggling to write a nested for loop but I'd really like to use purrr or something more elegant to create a dataframe with two columns: the subcat column, and a repeated column for the name for each element in the list.

Any help appreciated, even just pointing me to similar posts - thanks!

回答1:

You can try :

library(purrr)  

test1 <- flatten(test)
do.call(rbind.data.frame, map2(map_chr(test1, `[[`, 'name'), 
                               map(test1, `[[`, 'subcat'), cbind))

#  V1 V2
#1  A  1
#2  A  2
#3  A  3
#4  B  4
#5  B  5
#6  B  6

---

For the updated data :

library(tidyverse)
enframe(test) %>%  unnest_longer(value)

# A tibble: 6 x 2
#  name  value
#  <chr> <chr>
#1 A     1    
#2 A     2    
#3 A     3    
#4 B     4    
#5 B     5    
#6 B     6   

回答2:

library(dplyr)
library(purrr)
library(tidyr)

test %>% 
  as_tibble() %>%                                  # dplyr
  mutate(category = map(category, as_tibble)) %>%  # purrr
  unnest(cols = "category") %>%                    # tidyr
  unnest(cols = "subcat")

# A tibble: 6 x 2
  name  subcat
  <chr> <chr> 
1 A     1     
2 A     2     
3 A     3     
4 B     4     
5 B     5     
6 B     6  

This approach converts your list into a dataframe, then each list-element of it into a dataframe, then unnests them successively.

回答3:

We can do this in base R with stack

stack(test)[2:1]
#   ind values
#1   A      1
#2   A      2
#3   A      3
#4   B      4
#5   B      5
#6   B      6

---

Or using unlist/data.frame

data.frame(name = rep(names(test), lengths(test)), val = unlist(test))

来源：https://stackoverflow.com/questions/59905687/nested-list-to-dataframe-using-purrr-map