Fix detection of NaN in median() (#73)

There is no reliable way to know only from the array eltype whether entries
support `isnan` or not. Better leave to the compiler to optimize out the
`isa Number` check when possible.

src/Statistics.jl

@@ -805,7 +805,7 @@ Like [`median`](@ref), but may overwrite the input vector.
 function median!(v::AbstractVector)
     isempty(v) && throw(ArgumentError("median of an empty array is undefined, $(repr(v))"))
     eltype(v)>:Missing && any(ismissing, v) && return missing
-    (eltype(v)<:AbstractFloat || eltype(v)>:AbstractFloat) && any(isnan, v) && return convert(eltype(v), NaN)
+    any(x -> x isa Number && isnan(x), v) && return convert(eltype(v), NaN)
     inds = axes(v, 1)
     n = length(inds)
     mid = div(first(inds)+last(inds),2)

test/runtests.jl

@@ -67,6 +67,15 @@ end
     @test @inferred(median(Float16[1, 2, 3]))   === Float16(2)
     @test @inferred(median(Float32[1, 2, NaN])) === NaN32
     @test @inferred(median(Float32[1, 2, 3]))   === 2.0f0
+
+    # custom type implementing minimal interface
+    struct A
+        x
+    end
+    Statistics.middle(x::A, y::A) = A(middle(x.x, y.x))
+    Base.isless(x::A, y::A) = isless(x.x, y.x)
+    @test median([A(1), A(2)]) === A(1.5)
+    @test median(Any[A(1), A(2)]) === A(1.5)
 end
 
 @testset "mean" begin