Add index function diurnal_temperature_range (closes #153)

climix/etc/index_definitions.yml

@@ -1477,7 +1477,7 @@ indices:
       low_data: tasmin
       high_data: tasmax
     index_function:
-      name: dtr
+      name: diurnal_temperature_range
       parameters:
     ET:
       short_name: "dtr"

climix/etc/metadata.yml

@@ -33,6 +33,12 @@ index_functions:
       condition:
         kind: operator
 
+  diurnal_temperature_range:
+    description: |
+      This index function takes two inputs, low_data and high_data, i.e.
+      daily minimum and maximum temperature.
+      From this it calculated the average diurnal temperature range.
+
   first_occurrence:
     description: |
       Calculates the first time some condition is met.

climix/index_functions/__init__.py

@@ -3,6 +3,7 @@
 from .index_functions import (  # noqa: F401
     CountLevelCrossings,
     CountOccurrences,
+    DiurnalTemperatureRange,
     FirstOccurrence,
     LastOccurrence,
     SpellLength,

climix/index_functions/index_functions.py

@@ -56,6 +56,25 @@ class CountOccurrences(ThresholdMixin, IndexFunction):
         return res.astype('float32')
 
 
+class DiurnalTemperatureRange(IndexFunction):
+    def __init__(self):
+        super().__init__(units=Unit('degree_Celsius'))
+
+    def prepare(self, input_cubes):
+        props = {(cube.dtype, cube.units, cube.standard_name)
+                 for cube in input_cubes.values()}
+        assert len(props) == 1
+        dtype, units, standard_name = props.pop()
+        assert units in [Unit('Kelvin'), Unit('degree_Celsius')]
+        super().prepare(input_cubes)
+
+    def call_func(self, data, axis, **kwargs):
+        res = (data['high_data'] - data['low_data']).mean(axis=axis)
+        return res.astype('float32')
+
+    lazy_func = call_func
+
+
 class FirstOccurrence(ThresholdMixin, IndexFunction):
     def __init__(self, threshold, condition):
         super().__init__(threshold, condition, units=Unit('days'))

setup.py

@@ -60,6 +60,7 @@ setuptools.setup(
             'statistics=climix.index_functions:Statistics',
             'thresholded_statistics=climix.index_functions:ThresholdedStatistics',
             'temperature_sum=climix.index_functions:TemperatureSum',
+            'diurnal_temperature_range=climix.index_functions:DiurnalTemperatureRange',
         ],
     },
     project_urls={