r - Flatten list column in data frame with ID column

Question

My data frame contains the output of a survey with a select multiple question type. Some cells have multiple values.

df <- data.frame(a=1:3,b=I(list(1,1:2,1:3)))
df
  a       b
1 1       1
2 2    1, 2
3 3 1, 2, 3

I would like to flatten out the list to obtain the following output:

df
  a       b
1 1       1
2 2       1
3 2       2
4 3       1
5 3       2
6 3       3

should be easy but somehow I can't find the search terms. thanks.

Answer 1

You can just use unnest from "tidyr":

library(tidyr)
unnest(df, b)
#   a b
# 1 1 1
# 2 2 1
# 3 2 2
# 4 3 1
# 5 3 2
# 6 3 3