Data.table - left outer join on multiple tables

Question

Suppose you have data like

fruits <- data.table(FruitID=c(1,2,3), Fruit=c(\"Apple\", \"Banana\", \"Strawberry\"))
colors <- data.table(ColorID=c(1,2,3,         


        

Answer 1

I just committed a new feature in data.table, v1.9.5, with which we can join without setting keys (that is, specify the columns to join by directly, without having to use setkey() first):

With that, this is simply:

require(data.table) # v1.9.5+
fruits[tastes, on="FruitID"][colors, on="FruitID"] # no setkey required
#    FruitID      Fruit TasteID  Taste ColorID  Color
# 1:       1      Apple       1 Sweeet       1    Red
# 2:       1      Apple       2   Sour       1    Red
# 3:       1      Apple       1 Sweeet       2 Yellow
# 4:       1      Apple       2   Sour       2 Yellow
# 5:       1      Apple       1 Sweeet       3  Green
# 6:       1      Apple       2   Sour       3  Green
# 7:       2         NA      NA     NA       4 Yellow
# 8:       3 Strawberry       3  Sweet       5    Red