Number of Data in survey class.

SimPEG/Survey.py

@@ -47,6 +47,13 @@ class BaseSurvey(object):
         self.prob._survey = None
         self._prob = None
 
+    @property
+    def nD(self):
+        """Number of data."""
+        if hasattr(self, 'dobs'):
+            return self.dobs.size
+        raise NotImplemented('Number of data is unknown.')
+
     @property
     def ispaired(self): return self.prob is not None