fix cat empty features (#286)

Author: CarloLucibello

src/GNNGraphs/datastore.jl

@@ -106,10 +106,10 @@ function Base.getproperty(ds::DataStore, s::Symbol)
 end
 
 function Base.setproperty!(ds::DataStore, s::Symbol, x)
-    @assert s!=:_n "cannot set _n directly"
-    @assert s!=:_data "cannot set _data directly"
-    if getn(ds) > 0
-        @assert numobs(x)==getn(ds) "expected (numobs(x) == getn(ds)) but got $(numobs(x)) != $(getn(ds))"
+    @assert s != :_n "cannot set _n directly"
+    @assert s != :_data "cannot set _data directly"
+    if getn(ds) >= 0
+        @assert numobs(x) == getn(ds) "expected (numobs(x) == getn(ds)) but got $(numobs(x)) != $(getn(ds))"
     end
     return getdata(ds)[s] = x
 end
@@ -164,7 +164,7 @@ function MLUtils.getobs(ds::DataStore,
                         i::AbstractVector{T}) where {T <: Union{Integer, Bool}}
     newdata = getobs(getdata(ds), i)
     n = getn(ds)
-    if n > -1
+    if n >= 0
         if length(ds) > 0
             n = numobs(newdata)
         else
@@ -180,14 +180,14 @@ end
 
 function cat_features(ds1::DataStore, ds2::DataStore)
     n1, n2 = getn(ds1), getn(ds2)
-    n1 = n1 > 0 ? n1 : 1
-    n2 = n2 > 0 ? n2 : 1
+    n1 = n1 >= 0 ? n1 : 1
+    n2 = n2 >= 0 ? n2 : 1
     return DataStore(n1 + n2, cat_features(getdata(ds1), getdata(ds2)))
 end
 
 function cat_features(dss::AbstractVector{DataStore}; kws...)
     ns = getn.(dss)
-    ns = map(n -> n > 0 ? n : 1, ns)
+    ns = map(n -> n >= 0 ? n : 1, ns)
     return DataStore(sum(ns), cat_features(getdata.(dss); kws...))
 end
 

test/GNNGraphs/datastore.jl

@@ -39,6 +39,24 @@ end
     @test_throws KeyError ds.n
 end
 
+@testset "cat empty" begin
+    ds1 = DataStore(2, (:x => rand(2)))
+    ds2 = DataStore(1, (:x => rand(1)))
+    dsempty = DataStore(0, (:x => rand(0)))
+
+    ds = GNNGraphs.cat_features(ds1, ds2)
+    @test getn(ds) == 3
+    ds = GNNGraphs.cat_features(ds1, dsempty)
+    @test getn(ds) == 2
+
+    # issue #280
+    g = GNNGraph([1], [2])
+    h = add_edges(g, Int[], Int[])  # adds no edges
+    @test getn(g.edata) == 1
+    @test getn(h.edata) == 1
+end
+
+
 @testset "gradient" begin
     ds = DataStore(10, (:x => rand(10), :y => rand(2, 10)))