Adding multiple new columns to dataframe?

[bkamins]

@LasseKatten

I intend to populate that dataframe row by row in the next step, hence why I need an empty dataframe with specified columns.

1. You do not need to know the list of columns upfront as push! has cols=:union option that will handle this
2. If you know the list of columns upfront then it is easier to write:

DataFrame([:c1, :c2, :c3] .=> Ref([]))

or

DataFrame(fill([], 3), [:c1, :c2, :c3])

(in my original answer I thought you do not know the list of columns when creating a data frame)