groupby doesn't transform Vector of Tuples into separate Columns

[piever]

When groupby takes as input a function that returns NamedTuples, it does not expand the output to separate columns in some cases:

julia> using IndexedTables

julia> df = table(rand(Bool, 100), rand(100), rand(100), names = [:x, :y, :z], pkey = :x);

julia> groupby(t -> map(mean, columns(table(t))), df, select = (:y, :z))
Table with 2 rows, 2 columns:
x      #7
───────────────────────────────────
false  (y = 0.477451, z = 0.48867)
true   (y = 0.575163, z = 0.484047)

When instead one would expect:

julia> using IndexedTables

julia> df = table(rand(Bool, 100), rand(100), rand(100), names = [:x, :y, :z], pkey = :x);

julia> groupby(t -> map(mean, columns(table(t))), df, select = (:y, :z))
Table with 2 rows, 2 columns:
x      y          z
───────────────────────────────────
false  0.477451   0.48867
true   0.575163   0.484047

[piever]

Fixed by #150