Index function statistics (closes #79)

climix/etc/metadata.yml

@@ -65,6 +65,13 @@ index_functions:
       reducer:
         kind: reducer
 
+  statistics:
+    description: |
+      Calculates a simple statistic of the data.
+    parameters:
+      reducer:
+        kind: reducer
+
   thresholded_statistics:
     description: |
       Calculates a simple statistic of the data for which some condition is met.

climix/index_functions.py

@@ -241,6 +241,27 @@ class SpellLength:
         return float(res)
 
 
+class Statistics:
+    def __init__(self, reducer):
+        self.reducer = NUMPY_REDUCERS[reducer]
+        self.lazy_reducer = DASK_REDUCERS[reducer]
+        self.extra_coords = []
+
+    def prepare(self, input_cube):
+        self.standard_name = input_cube.standard_name
+        self.units = input_cube.units
+
+    def call_func(self, data, axis, **kwargs):
+        axis = normalize_axis(axis, data.ndim)
+        res = self.reducer(data, axis=axis)
+        return res.astype('float32')
+
+    def lazy_func(self, data, axis, **kwargs):
+        axis = normalize_axis(axis, data.ndim)
+        res = self.lazy_reducer(data, axis=axis)
+        return res.astype('float32')
+
+
 class ThresholdedStatistics:
     def __init__(self, threshold, condition, reducer):
         self.threshold = threshold

setup.py

@@ -55,6 +55,7 @@ setuptools.setup(
             'first_occurrence=climix.index_functions:FirstOccurrence',
             'last_occurrence=climix.index_functions:LastOccurrence',
             'spell_length=climix.index_functions:SpellLength',
+            'statistics=climix.index_functions:Statistics',
             'thresholded_statistics=climix.index_functions:ThresholdedStatistics',
         ],
     },