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rlistdataframedata.tableaggregate

Counting unique list items

Assuming I have a datatable dt.recipes which consists of lists with various items, for example:

recipe_id     ingredients
1             apple, banana, cucumber, water
2             apple, meat, water
3             water

How can I create a table, counting the amount of unique items present in dt.recipes$ingredients? In other words, I am looking for a result similar to this:

ingredient    count
water         3
apple         2
banana        1
cucumber      1
meat          1

Any pointers would be greatly appreciated, thanks in advance!

Solution

  • A data.table way could be

    library(data.table)
dt[, .(table(unlist(ingredients)))]
#         V1 N
#1:    apple 2
#2:   banana 1
#3: cucumber 1
#4:     meat 1
#5:    water 3

    data

    dt <- data.table(
  "recipe_id" = 1:3,
  "ingredients" = list(
    c("apple", "banana", "cucumber", "water"),
    c("apple", "meat", "water"),
    c("water")
  )
)