Does Julia have equivalent of Python: DF.column.map( dict )

General Usage
9

This is a compilation time thing. Creating a new anonymous function has a fixed compilation cost, so map(t -> ..., x) is slow

julia> x = rand(1:5, 100);

julia> d = Dict(1 => "A", 2 => "B", 3 => "C", 4 => "D", 5 => "E");

julia> @time getindex.(Ref(d), x);
  0.144137 seconds (172.92 k allocations: 9.074 MiB, 42.83% gc time)

julia> @time getindex.(Ref(d), x);
  0.000016 seconds (4 allocations: 976 bytes)

julia> @time map(xi -> d[xi], x);
  0.081783 seconds (98.49 k allocations: 5.256 MiB)

julia> @time map(xi -> d[xi], x);
  0.078627 seconds (55.19 k allocations: 2.922 MiB)

julia> get_from_d = let d = d
       xi -> d[xi]
       end;

julia> @time map(get_from_d, x);
  0.043167 seconds (43.72 k allocations: 2.272 MiB)

julia> @time map(get_from_d, x);
  0.000024 seconds (2 allocations: 928 bytes)

This re-compilation problem only shows up in global scope, though.

julia> function get_from_d_wrapper(d, x)
       map(xi -> d[xi], x)
       end;

julia> @time get_from_d_wrapper(d, x);
  0.037174 seconds (46.42 k allocations: 2.426 MiB)

julia> @time get_from_d_wrapper(d, x);
  0.000006 seconds (1 allocation: 896 bytes)
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