CODEWITHSUNDEEP
juliadplyr
Francis Smart
Francis Smart

Reputation: 4065

Mutate DataFrames in Julia

Looking for a function that works like by but doesn't collapse my DataFrame. In R I would use dplyr's groupby(b) %>% mutate(x1 = sum(a)). I don't want to lose information from the table such as that in variable :c.

mydf = DataFrame(a = 1:4, b = repeat(1:2,2), c=4:-1:1)
bypreserve(mydf, :b,  x -> sum(x.a))
│ Row │ a     │ b     │ c     │ x1
│     │ Int64 │ Int64 │ Int64 │Int64 
├─────┼───────┼───────┼───────┤───────
│ 1   │ 1     │ 1     │ 4     │ 4
│ 2   │ 2     │ 2     │ 3     │ 6
│ 3   │ 3     │ 1     │ 2     │ 4
│ 4   │ 4     │ 2     │ 1     │ 6

Upvotes: 3

Views: 735

Answers (1)

Bogumił Kamiński
Bogumił Kamiński

Reputation: 69949

Adding this functionality is discussed, but I would say that it will take several months to be shipped (the general idea is to allow select to have groupby keyword argument + also add transform function that will work like select but preserve columns of the source data frame).

For now the solution is to use join after by:

join(mydf, by(mydf, :b, x1 = :a => sum), on=:b)

Upvotes: 4

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