fix threaded map over one element

Author: Michael Abbott

src/SliceMap.jl

@@ -297,7 +297,11 @@ function threadmap(f::Function, vw::AbstractVector...)
     length(first(vw))==0 && error("can't map over empty vector, sorry")
     length(vw)==2 && (isequal(length.(vw)...) || error("lengths must be equal"))
     out1 = f(first.(vw)...)
-    _threadmap(out1, f, vw...)
+    if length(vw) > 1
+        _threadmap(out1, f, vw...)
+    else
+        [out1]
+    end
 end
 # NB function barrier. Plus two versions:
 @static if VERSION < v"1.3"

test/runtests.jl

@@ -39,6 +39,11 @@ Zygote.refresh()
     @test res ≈ jcols(fun, mat)
     @test grad ≈ Zygote.gradient(m -> sum(sin, jcols(fun, m)), mat)[1]
 
+    # Case of length 1, was an error for _threadmap
+    @test res[:,1:1] ≈ mapcols(fun, mat[:, 1:1])
+    @test res[:,1:1] ≈ tmapcols(fun, mat[:, 1:1])
+    @test res[:,1:1] ≈ ThreadMapCols(fun, mat[:, 1:1])
+
 end
 @testset "columns -> scalar" begin
 
@@ -171,7 +176,7 @@ end
 
     rec(store) = x -> (push!(store, first(x)); x)
     A = [1,1,1] .* (1:5)'
-    
+
     store = []
     slicemap(rec(store), A; dims=1)
     @test store == 1:5