Fix computed_metrics attribute initialization

physutils/physio.py

@@ -342,7 +342,7 @@ def __init__(
                 reject=np.empty(0, dtype=int),
             )
         self._suppdata = None if suppdata is None else np.asarray(suppdata).squeeze()
-        self._computed_metrics = []
+        self._computed_metrics = dict()
 
     def __array__(self):
         return self.data