[data] DSS: adds concantenate

data.py

@@ -67,6 +67,10 @@ class SKDict(dict):
         keys.update(*(inst.keys() for inst in insts))
         return cls({key: tuple(inst.get(key) for inst in insts) for key in keys})
 
+    @classmethod
+    def concatenate(cls, *insts):
+        return cls.zip(*insts).map(lambda x: np.concatenate(x))
+
     def only(self, *keys):
         return self.__class__({key: self[key] for key in keys})