Lazily convert to Unitful

Units are only converted to an Unitful object when converting to
different units.

ext/ClimaAnalysisUnitfulExt.jl

@@ -49,8 +49,9 @@ function Var.convert_units(
     new_units::AbstractString;
     conversion_function = nothing,
 )
-    has_unitful_units =
-        Var.has_units(var) && (var.attributes["units"] isa Unitful.Units)
+    maybe_unitful_units =
+        Var.has_units(var) && (Var.units(var) |> Var._maybe_convert_to_unitful)
+    has_unitful_units = maybe_unitful_units isa Unitful.Units
     new_units_maybe_unitful = Var._maybe_convert_to_unitful(new_units)
     new_units_are_unitful = new_units_maybe_unitful isa Unitful.Units
 
@@ -60,7 +61,7 @@ function Var.convert_units(
         convert_function =
             data -> _converted_data_unitful(
                 data,
-                var.attributes["units"],
+                maybe_unitful_units,
                 new_units_maybe_unitful,
             )
     else
@@ -72,7 +73,7 @@ function Var.convert_units(
 
     new_data = convert_function(var.data)
     new_attribs = copy(var.attributes)
-    # The constructor will take care of converting new_units to Unitful
+    # Units will be a string and not Unitful
     new_attribs["units"] = new_units
 
     return Var.OutputVar(new_attribs, var.dims, var.dim_attributes, new_data)

src/Var.jl

@@ -186,18 +186,6 @@ function OutputVar(attribs, dims, dim_attribs, data)
         end
     end
 
-    function _maybe_process_key_value(k, v)
-        k != "units" && return k => v
-        return k => _maybe_convert_to_unitful(v)
-    end
-
-    # Recreating an object to ensure that the type is correct
-    if !isempty(attribs)
-        attribs = Dict(_maybe_process_key_value(k, v) for (k, v) in attribs)
-    end
-
-    # TODO: Support units for dimensions too
-
     return OutputVar(
         attribs,
         OrderedDict(dims),

test/test_Var.jl

@@ -28,8 +28,8 @@ import Dates
         data,
     )
 
-    @test ClimaAnalysis.units(var_with_unitful) == "m s^-1"
-    @test var_with_unitful.attributes["units"] == u"m" / u"s"
+    @test ClimaAnalysis.units(var_with_unitful) == "m/s"
+    @test var_with_unitful.attributes["units"] == "m/s"
 
     # Unparsable unit
     attribs = Dict("long_name" => "hi", "units" => "bob")
@@ -1160,7 +1160,7 @@ end
     @test squared_error_var.data == (data_ones - data_threes) .^ 2
     @test ClimaAnalysis.short_name(squared_error_var) == "(sim-obs)^2_short"
     @test ClimaAnalysis.long_name(squared_error_var) == "(SIM - OBS)^2 short"
-    @test ClimaAnalysis.units(squared_error_var) == "kg^2"
+    @test ClimaAnalysis.units(squared_error_var) == "(kg)^2"
 
     # Flip order in squared_error and check computations
     squared_error_var = ClimaAnalysis.squared_error(var_threes, var_ones)
@@ -1201,7 +1201,7 @@ end
     var_unitful = ClimaAnalysis.squared_error(var_unitful, var_unitful)
     var_not_unitful =
         ClimaAnalysis.squared_error(var_not_unitful, var_not_unitful)
-    @test ClimaAnalysis.units(var_unitful) == "(kg^2 m^-1)^2"
+    @test ClimaAnalysis.units(var_unitful) == "(kg^2/m)^2"
     @test ClimaAnalysis.units(var_not_unitful) == "(wacky/weird^2)^2"
 end