Use meaningful element type in tabular sets

src/categorical_algebra/DataMigrations.jl

@@ -149,7 +149,7 @@ function migrate(X::ACSet, F::ConjSchemaMigration)
     Fc = diagram(ob_map(F, c))
     lim = limit(compose(Fc, X, strict=false), BipartiteLimit())
     J = dom(Fc)
-    names = Tuple(Symbol(ob_name(J, j)) for j in ob_generators(J))
+    names = Tuple(column_name(ob_name(J, j)) for j in ob_generators(J))
     TabularSet(NamedTuple{names}(Tuple(map(collect, legs(lim)))))
   end
   funcs = make_map(hom_generators(tgt_schema)) do f
@@ -165,6 +165,9 @@ function migrate(X::ACSet, F::ConjSchemaMigration)
   FinDomFunctor(sets, funcs, tgt_schema)
 end
 
+column_name(name) = Symbol(name)
+column_name(i::Integer) = Symbol("x$i") # Same default as DataFrames.jl.
+
 # FIXME: We should put this elsewhere and think more carefully about names.
 ob_name(C::FinCat, x) = x
 ob_name(C::FinCat, x::GATExpr) = nameof(x)

src/categorical_algebra/FinSets.jl

@@ -79,16 +79,26 @@ end
 
 """ Finite set whose elements are rows of a table.
 
-The underlying table should be compliant with Tables.jl.
+The underlying table should be compliant with Tables.jl. For the sake of
+uniformity, the rows are provided as named tuples, which assumes that the table
+is not "extremely wide". This should not be a major limitation in practice but
+see the Tables.jl documentation for further discussion.
 """
-@auto_hash_equals struct TabularSet{Table} <: FinSet{Table,Any}
+@auto_hash_equals struct TabularSet{Table,Row} <: FinSet{Table,Row}
   table::Table
+
+  function TabularSet(table::Table) where Table
+    schema = Tables.schema(table)
+    new{Table,NamedTuple{schema.names,Tuple{schema.types...}}}(table)
+  end
 end
 
 FinSet(nt::NamedTuple) = TabularSet(nt)
 
-Base.iterate(set::TabularSet, args...) = iterate(Tables.rows(set.table), args...)
+Base.iterate(set::TabularSet, args...) =
+  iterate(Tables.namedtupleiterator(set.table), args...)
 Base.length(set::TabularSet) = Tables.rowcount(set.table)
+Base.collect(set::TabularSet) = Tables.rowtable(set.table)
 
 function Base.show(io::IO, set::TabularSet)
   print(io, "TabularSet(")

test/categorical_algebra/DataMigrations.jl

@@ -94,10 +94,8 @@ X = path_graph(Graph, 5)
 Y = migrate(X, F)
 @test length(Y(V)) == 5
 @test length(Y(E)) == 3
-@test Y(src)((v=3, e₁=2, e₂=3)) |> only == 2
-@test Y(tgt)((v=3, e₁=2, e₂=3)) |> only == 4
-@test Y(src)((3, 2, 3)) |> only == 2
-@test Y(tgt)((3, 2, 3)) |> only == 4
+@test Y(src)((x1=3, x2=2, x3=3)) == (x1=2,)
+@test Y(tgt)((x1=3, x2=2, x3=3)) == (x1=4,)
 
 # Same query, but with `@migration` macro.
 F = @migration TheoryGraph TheoryGraph begin

test/categorical_algebra/FinSets.jl

@@ -23,8 +23,9 @@ set = FinSet(Set(1:2:5))
 
 # Tables as sets.
 set = FinSet((x=[1,3,5], y=["a","b","c"]))
+@test eltype(set) == NamedTuple{(:x,:y),Tuple{Int,String}}
 @test length(set) == 3
-@test map(NamedTuple, set) == [(x=1, y="a"), (x=3, y="b"), (x=5, y="c")]
+@test collect(set) == [(x=1, y="a"), (x=3, y="b"), (x=5, y="c")]
 @test startswith(sshow(set), "TabularSet(")
 @test startswith(sshow(MIME("text/plain"), set), "3-element TabularSet")
 @test startswith(sshow(MIME("text/html"), set), "<div")