Vectorized “in” function in julia?

Question

I often want to loop over a long array or column of a dataframe, and for each item, see if it is a member of another array. Rather than doing

giant_list =          


        

Answer 1

There are a handful of modern (i.e. Julia v1.0) solutions to this problem:

First, an update to the scalar strategy. Rather than using a 1-element tuple or array, scalar broadcasting can be achieved using a Ref object:

julia> in.(giant_list, Ref(good_letters))
3-element BitArray{1}:
  true
 false
 false

This same result can be achieved by broadcasting the infix ∈ (\inTAB) operator:

julia> giant_list .∈ Ref(good_letters)
3-element BitArray{1}:
  true
 false
 false

Additionally, calling in with one argument creates a Base.Fix2, which may later be applied via a broadcasted call. This seems to have limited benefits compared to simply defining a function, though.

julia> is_good1 = in(good_letters);
       is_good2(x) = x in good_letters;

julia> is_good1.(giant_list)
3-element BitArray{1}:
  true
 false
 false

julia> is_good2.(giant_list)
3-element BitArray{1}:
  true
 false
 false

All in all, using .∈ with a Ref will probably lead to the shortest, cleanest code.