Most efficient way to compute number of rows in each group using JuliaDB?

Specific Domains Data
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Suppose a is a JuliaDB table, is the below the best (most efficient) way to compute the number of rows per group?

using LambdaFn, DataFrames, JuliaDB
a = DataFrame(Column1 = rand(["a", "b", "c"], 1_000), b = rand(1000)) |> JuliaDB.table

@time JuliaDB.groupby(@λ(size(_,1)), a, :Column1)