Implement averaging of ResultLists (#162)

* Implement averaging of ResultLists
* Move averaging into a new class

src/elli/result.py

@@ -19,7 +19,8 @@
 
 To make handling multiple experiments easier, they can be grouped into a list and provided
 to a ResultList object. It provides the same methods for data output as the single Result.
-The Output is returned as array over the list of results.
+The Output is returned as array over the list of results. If needed, these arrays can be
+averaged and used like a Result object for fitting.
 """
 from typing import List
 
@@ -458,6 +459,7 @@ def __init__(self, results: List[Result] = None) -> None:
 
         Args:
             results (List[Result], optional): List of results to store. Defaults to None.
+            mean (bool, optional): Returns the average of all results. Defaults to False.
         """
         if results is None:
             self.results = []
@@ -493,9 +495,46 @@ def __getattr__(self, name: str) -> npt.NDArray:
                 'psi', 'delta', 'rho':
                     Reduced ellipsometry parameters,
                     the whole matrices are returned by 'psi_matrix'.
+                'mean.name' : Returns averaged values for the requested variable,
+                    e.g. 'mean.psi'.
 
         Returns:
             npt.NDArray: Array of data.
         """
 
+        if name == "mean":
+            return AveragedResultList(self.results)
+
         return np.squeeze(np.array([getattr(result, name) for result in self.results]))
+
+
+class AveragedResultList(ResultList):
+    """ResultList with averaging over all results.
+    Can be used as drop-in replacement for Result objects, if for example
+    thickness inhomogeneities need to be simulated.
+    """
+
+    def __getattr__(self, name: str) -> npt.NDArray:
+        """Returns the data for the requested variable 'name' of all results.
+
+        Args:
+            name (str): Variable name to return.
+                Examples for 'name'...
+                'r_sp' : Amplitude reflection coefficient from 's' to 'p' polarization.
+                'r_LR' : Reflection from circular right to circular left polarization.
+                'T_pp' : Power transmission coefficient from 'p' to 'p' polarization.
+                'Ψ_ps', 'Δ_pp' : Ellipsometry parameters.
+                'psi', 'delta', 'rho':
+                    Reduced ellipsometry parameters,
+                    the whole matrices are returned by 'psi_matrix'.
+
+        Returns:
+            npt.NDArray: Array of data.
+        """
+
+        if name == "mean":
+            raise ValueError(
+                "The ResultList is already averaged and can't be averaged again."
+            )
+
+        return np.mean(super().__getattr__(name), axis=0)

tests/test_result.py

@@ -1,8 +1,8 @@
 """Tests for the result class"""
 
+import elli
 import numpy as np
 from pytest import fixture, raises
-import elli
 
 
 @fixture
@@ -40,3 +40,13 @@ def test_delta_range_error_on_invalid_range(result):
 
     with raises(ValueError):
         result.as_delta_range(20, 180)
+
+
+def test_resultlist_shape(result):
+    result_list = elli.ResultList([result, result, result])
+
+    assert len(result_list) == 3
+    assert np.shape(result_list.delta) == (3, 50)
+
+    assert np.shape(result_list.mean.delta) == (50,)
+    assert np.allclose(result_list.mean.delta, result.delta)