Fix dimension ordering when converting a DataArray to DimArray (#971)

Previously the code would temporarily store the dimension => lookup mapping in a
Dict, but that doesn't maintain insertion order. So later on it was possible for
the DimArray to be created with the dimensions in the wrong order, which would
cause an exception.

Author: JamesWrigley

ext/DimensionalDataPythonCall.jl

@@ -53,20 +53,20 @@ function PythonCall.pyconvert(::Type{DimArray}, x::Py, d=nothing)
 
     dim_names = Symbol.(collect(x.dims))
     coord_names = Symbol.(collect(x.coords.keys()))
-    lookups_dict = Dict{Symbol, Any}()
-    for dim in dim_names
+    lookups_vec = Pair{Symbol, Any}[]
+    for dim in reverse(dim_names) # Iterate in reverse order because of row/col major
         if dim in coord_names
             coord = getproperty(x, dim).data
             coord_type = dtype2type(string(coord.dtype.name))
             coord_ndim = pyconvert(Int, coord.ndim)
 
-            lookups_dict[dim] = pyconvert(Array{coord_type, coord_ndim}, coord)
+            push!(lookups_vec, dim => pyconvert(Array{coord_type, coord_ndim}, coord))
         else
-            lookups_dict[dim] = NoLookup()
+            push!(lookups_vec, dim => NoLookup())
         end
     end
 
-    lookups = NamedTuple(lookups_dict)
+    lookups = NamedTuple(lookups_vec)
 
     metadata = pyconvert(Dict, x.attrs)
 

test/xarray.jl

@@ -38,6 +38,14 @@ x2 = xr.DataArray(data2,
 
     @test_throws ArgumentError pyconvert(DimArray, xr)
     @test pyconvert(DimArray, xr, 42) == 42
+
+    # Sanity test for higher-dimensional arrays
+    x3 = xr.DataArray(rand(2, 5, 5, 3),
+                      dims=("w", "x", "y", "z"),
+                      coords=Dict("w" => [1, 2], "z" => [1, 2, 3]))
+    y = pyconvert(DimArray, x3)
+    @test lookup(y, :w) == [1, 2]
+    @test lookup(y, :z) == [1, 2, 3]
 end
 
 @testset "Dataset to DimStack" begin