fixes the issue #54

data/dimensionless_mappings.yaml

@@ -3,3 +3,5 @@
 #   cmor_unit_string: pint_friendly_SI_units
 so:
   "0.001": g/kg
+so:
+  "0.001": g/kg

examples/sample.yaml

@@ -14,7 +14,7 @@ pymorize:
   fixed_jobs: 12
   # minimum_jobs: 8
   # maximum_jobs: 30
-  dimensionless_mapping_table: ./data/dimensionless_mappings.yaml
+  dimensionless_mapping_table: ../data/dimensionless_mappings.yaml
 rules:
   - name: paul_example_rule
     description: "You can put some text here"

src/pymorize/units.py

@@ -3,15 +3,10 @@
 In case the units in model files differ from CMIP Tables, this module attempts to
 convert them automatically.
 
-In case of missing units in either model files or CMIP Tables, this module can
-not convert from a dimentionless base to something with dimension. Dealing with
-such thing have to done with `action` section in the Rules module on a per
-variable basis.
-
-Additionally, the cmip frequencies are mapped here. The CMIP6 frequency
-names and corresponding number of days are available as a dictionary in the
-``CMIP_FREQUENCIES`` variable. Assignment of these frequencies to the unit registry
-can be done with the ``assign_frequency_to_unit_registry`` function.
+Conversion to-or-from a dimensionless quantity is ambiguous. In this case,
+provide a mapping of what this dimensionless quantity represents and that
+is used for the conversion. `data/dimensionless_mappings.yaml` contains some
+examples on how the mapping is written.
 """
 
 import re
@@ -27,19 +22,12 @@
 import xarray as xr
 from chemicals import periodic_table
 
-from .frequency import CMIP_FREQUENCIES
 from .logging import logger
 from .rule import Rule
 
 ureg = pint_xarray.unit_registry
 
 
-def assign_frequency_to_unit_registry():
-    """Assign the CMIP6 frequencies to the unit registry."""
-    for freq_name, days in CMIP_FREQUENCIES.items():
-        ureg.define(f"{freq_name} = {days} * d")
-
-
 def handle_chemicals(
     s: Union[str, None] = None, pattern: Pattern = re.compile(r"mol(?P<symbol>\w+)")
 ):
@@ -110,15 +98,24 @@ def handle_unit_conversion(da: xr.DataArray, rule: Rule) -> xr.DataArray:
     model_unit = rule.get("model_unit")
     from_unit = da.attrs.get("units")
     if model_unit is not None:
-        logger.debug(
+        logger.info(
             f"using user defined unit ({model_unit}) instead of ({from_unit}) from DataArray "
         )
         from_unit = model_unit
     handle_chemicals(from_unit)
     handle_chemicals(to_unit)
     new_da = da.pint.quantify(from_unit)
-    logger.debug(f"Converting units: {from_unit} -> {to_unit}")
-    new_da = new_da.pint.to(to_unit).pint.dequantify()
+    dimless = rule.get("dimensionless_unit_mappings", {})
+    cmor_variable = rule.get("cmor_variable")
+    if cmor_variable in dimless:
+        _to_unit = dimless[cmor_variable][to_unit]
+    else:
+        _to_unit = to_unit
+    if _to_unit == to_unit:
+        logger.info(f"Converting units: ({da.name} -> {cmor_variable}) {from_unit} -> {to_unit}")
+    else:
+        logger.info(f"Converting units: ({da.name} -> {cmor_variable}) {from_unit} -> {_to_unit} ({to_unit})")
+    new_da = new_da.pint.to(_to_unit).pint.dequantify()
     if new_da.attrs.get("units") != to_unit:
         logger.debug(
             "Pint auto-unit attribute setter different from requested unit string, setting manually."