将具有不同长度的向量的列表转换为数据帧

Question

I'm trying to convert a list containing multiple vectors of different length (of type factor) to a dataframe that has equal numbers of rows as elements in list and only one column.

Example:

ex.list <- (list(c("Tom", "Ron", "Joe"), c("Ron", "Joe"), c("Tom")))
ex.list <- lapply(ex.list, function(x) as.factor(x))

Desired output would be:

ex.list
        col1
    #1 Tom, Ron, Joe
    #2 Ron, Joe
    #3 Tom

When I call str(ex.list$col1) I'd like to get:

Factor w/3 levels: "Tom, Ron, Joe"

I don't have trouble to convert ex.list in a dataframe with 3 rows and 3 columns, but that isn't what I want.

What's the best approach here? Should I unlist and sequece the vector somehow into this 3 row, 1 column data frame? is there a handy function to do that?

Answer 1

df =  data.frame(col1 = unlist(lapply(ex.list, paste, collapse = ", ")))
> df
           col1
1 Tom, Ron, Joe
2      Ron, Joe
3           Tom

To get the unique names you'd have to run something like this

> unique(unlist(strsplit(as.character(df[ , 1]), ", ")))
[1] "Tom" "Ron" "Joe"

You're not going to be able to look at the levels of the factor with the way you want your data.frame setup.

Answer 2

You can use list columns with tidyr::nest and tidyr::unnest :

library(tidyverse)
df <- data.frame(id=seq_along(ex.list), col1 = unlist(lapply(ex.list, paste, collapse = ","))) %>%
  mutate(col1 = stringr::str_split(col1, ",")) %>%
  unnest %>% 
  mutate(col1=as.factor(col1)) %>% 
  nest(col1)

str(df)
Classes ‘tbl_df’, ‘tbl’ and 'data.frame':   3 obs. of  2 variables:
 $ id  : int  1 2 3
 $ data:List of 3
  ..$ :Classes ‘tbl_df’, ‘tbl’ and 'data.frame':    3 obs. of  1 variable:
  .. ..$ col1: Factor w/ 3 levels "Joe","Ron","Tom": 3 2 1
  ..$ :Classes ‘tbl_df’, ‘tbl’ and 'data.frame':    2 obs. of  1 variable:
  .. ..$ col1: Factor w/ 3 levels "Joe","Ron","Tom": 2 1
  ..$ :Classes ‘tbl_df’, ‘tbl’ and 'data.frame':    1 obs. of  1 variable:
  .. ..$ col1: Factor w/ 3 levels "Joe","Ron","Tom": 3