Add scalars as variables instead of attributes

Fixes #17

src/sdf_xarray/__init__.py

@@ -275,9 +275,12 @@ def _grid_species_name(grid_name: str) -> str:
                 continue
 
             if isinstance(value, Constant) or value.grid is None:
-                # No grid, so not physical data, just stick it in as an attribute
-                # This might have consequences when reading in multiple files?
-                attrs[key] = value.data
+                # No grid, so just a scalar
+                data_attrs = {}
+                if value.units is not None:
+                    data_attrs["units"] = value.units
+
+                data_vars[key] = Variable((), value.data, data_attrs)
                 continue
 
             if value.is_point_data:

src/sdf_xarray/sdf_interface.pyx

@@ -1,6 +1,7 @@
 cimport csdf
 
 import dataclasses
+import re
 import time
 
 from libc.string cimport memcpy
@@ -103,11 +104,14 @@ cdef class Mesh(Block):
         )
 
 
+_CONSTANT_UNITS_RE = re.compile(r"(?P<name>.*) \((?P<units>.*)\)$")
+
 @dataclasses.dataclass
 cdef class Constant:
     _id: str
     name: str
     data: int | str | float
+    units: str | None
 
     @staticmethod
     cdef Constant from_block(str name, csdf.sdf_block_t* block):
@@ -122,8 +126,16 @@ cdef class Constant:
         if block.datatype == csdf.SDF_DATATYPE_INTEGER8:
             data = (<csdf.int64_t*>block.const_value)[0]
 
+        # There's no metadata with e.g. units, but there's a
+        # convention to put one in brackets at the end of the name,
+        # if so, strip it off to give the name and units
+        units = None
+        if match := _CONSTANT_UNITS_RE.match(name):
+            name = match["name"]
+            units = match["units"]
+
         return Constant(
-            _id=block.id.decode("UTF-8"), name=name, data=data
+            _id=block.id.decode("UTF-8"), name=name, data=data, units=units
         )
 
     @property
@@ -203,7 +215,10 @@ cdef class SDFFile:
                 }
 
             elif block.blocktype == csdf.SDF_BLOCKTYPE_CONSTANT:
-                self.variables[name] = Constant.from_block(name, block)
+                # We modify the name to remove units, so convert it
+                # first so we can get the new name
+                constant = Constant.from_block(name, block)
+                self.variables[constant.name] = constant
 
             elif block.blocktype in (
                     csdf.SDF_BLOCKTYPE_PLAIN_MESH,

tests/example_files/input.deck

@@ -98,6 +98,7 @@ begin:output
 
   # Extended IO
   distribution_functions = always
+  absorption = always
 end:output
 
 

tests/test_basic.py

@@ -24,6 +24,13 @@ def test_basic():
         assert x_coord not in df.coords
 
 
+def test_constant_name_and_units():
+    with xr.open_dataset(EXAMPLE_FILES_DIR / "0000.sdf") as df:
+        name = "Absorption/Total Laser Energy Injected"
+        assert name in df
+        assert df[name].units == "J"
+
+
 def test_coords():
     with xr.open_dataset(EXAMPLE_FILES_DIR / "0010.sdf") as df:
         px_electron = "dist_fn/x_px/electron"
@@ -66,6 +73,10 @@ def test_multiple_files_one_time_dim():
     assert sorted(px_protons.coords) == sorted(("X_Particles/proton", "time"))
     assert px_protons.shape == (11, 1920)
 
+    absorption = df["Absorption/Total Laser Energy Injected"]
+    assert tuple(absorption.coords) == ("time",)
+    assert absorption.shape == (11,)
+
 
 def test_multiple_files_multiple_time_dims():
     df = open_mfdataset(
@@ -77,6 +88,7 @@ def test_multiple_files_multiple_time_dims():
     assert df["Electric Field/Ez"].shape == (1, 16)
     assert df["Particles/Px/proton"].shape == (1, 1920)
     assert df["Particles/Weight/proton"].shape == (2, 1920)
+    assert df["Absorption/Total Laser Energy Injected"].shape == (11,)
 
 
 def test_erroring_on_mismatched_jobid_files():

tests/test_cython.py

@@ -17,7 +17,7 @@ def test_sdffile():
 
         assert f.run_info["version"] == "4.19.3"
 
-        assert f.variables["Wall-time"].data == 0.0032005560000000002
+        assert f.variables["Wall-time"].data == 0.014211990000000008
 
 
 def test_sdffile_with_more_things():
@@ -29,7 +29,7 @@ def test_sdffile_with_more_things():
 
         assert f.run_info["version"] == "4.19.3"
 
-        assert f.variables["Wall-time"].data == 3.968111756
+        assert f.variables["Wall-time"].data == 4.068961859
 
 
 def test_variable_names():