Fix construction of Array from empty chains (#318)

Project.toml

@@ -3,7 +3,7 @@ uuid = "c7f686f2-ff18-58e9-bc7b-31028e88f75d"
 keywords = ["markov chain monte carlo", "probablistic programming"]
 license = "MIT"
 desc = "Chain types and utility functions for MCMC simulations."
-version = "4.13.0"
+version = "4.13.1"
 
 [deps]
 AbstractFFTs = "621f4979-c628-5d54-868e-fcf4e3e8185c"

src/constructors.jl

@@ -63,7 +63,8 @@ function Base.Array(
 end
 
 function to_matrix(chain::Chains)
-    return Matrix(reshape(permutedims(chain.value.data, (1, 3, 2)), :, size(chain, 2)))
+    x = permutedims(chain.value.data, (1, 3, 2))
+    return Matrix(reshape(x, size(x, 1) * size(x, 2), size(x, 3)))
 end
 
 function to_vector(chain::Chains)
@@ -79,4 +80,3 @@ function to_vector_of_matrices(chain::Chains)
     data = chain.value.data
     return [Matrix(data[:, :, i]) for i in axes(data, 3)]
 end
-

src/utils.jl

@@ -96,7 +96,7 @@ function merge_union(a::NamedTuple{an}, b::NamedTuple{bn}) where {an,bn}
                 :(getfield(b, $(QuoteNode(n))))
             end
         end
-        
+
         return :(NamedTuple{$names,$types}(($(values...),)))
     else
         names = Base.merge_names(an, bn)
@@ -113,7 +113,7 @@ function merge_union(a::NamedTuple{an}, b::NamedTuple{bn}) where {an,bn}
                 getfield(b, n)
             end
         end
-        
+
         return NamedTuple{names,types}(values)
     end
 end
@@ -179,8 +179,8 @@ function concretize(x::AbstractArray)
         return x
     else
         xnew = map(concretize, x)
-        T = mapreduce(typeof, promote_type, xnew)
-        if T <: eltype(xnew)
+        T = mapreduce(typeof, promote_type, xnew; init=Union{})
+        if T <: eltype(xnew) && T !== Union{}
             return convert(AbstractArray{T}, xnew)
         else
             return xnew

test/arrayconstructor_tests.jl

@@ -67,6 +67,11 @@ using MCMCChains, Test
         Array(chns[:a])
         Array(chns, [:parameters])
         Array(chns, [:parameters, :internals])
+
+        # empty chain: #317
+        empty_chain = chns[Symbol[]]
+        @test isempty(MCMCChains.to_matrix(empty_chain))
+        @test isempty(Array(empty_chain))
     end
     @testset "Accuracy" begin
         nchains = 5