Add `collapsed()` method on containers

lisainstrument/containers.py

@@ -46,6 +46,15 @@ class ForEachObject(abc.ABC):
         """
         return self.__class__(lambda mosa: transformation(mosa, self[mosa]))
 
+    def collapsed(self):
+        """Turn a numpy arrays containing identical elements into a scalar.
+
+        This method can be used to optimize computations when constant time series are involved.
+        """
+        return self.transformed(lambda _, x:
+            x[0] if isinstance(x, numpy.ndarray) and numpy.all(x == x[0]) else x
+        )
+
     def write(self, hdf5, dataset):
         """Write values in dataset on HDF5 file.