use LabelTensor, fix minor, docs

pina/label_tensor.py

@@ -81,11 +81,10 @@ class LabelTensor(torch.Tensor):
         Performs Tensor dtype and/or device conversion. For more details, see
         :meth:`torch.Tensor.to`.
         """
-        new_obj = LabelTensor([], self.labels)
-        tempTensor = super().to(*args, **kwargs)
-        new_obj.data = tempTensor.data
-        new_obj.requires_grad = tempTensor.requires_grad
-        return new_obj
+        tmp = super().to(*args, **kwargs)
+        new = self.__class__.clone(self)
+        new.data = tmp.data
+        return new
 
     def extract(self, label_to_extract):
         """
@@ -111,9 +110,23 @@ class LabelTensor(torch.Tensor):
         except ValueError:
             raise ValueError('`label_to_extract` not in the labels list')
 
-        extracted_tensor = LabelTensor(
-            self[:, indeces],
-            [self.labels[idx] for idx in indeces]
-        )
+        new_data = self[:, indeces].float()
+        new_labels = [self.labels[idx] for idx in indeces]
+        extracted_tensor = LabelTensor(new_data, new_labels)
 
         return extracted_tensor
+
+    def append(self, lt):
+        """
+        Return a copy of the merged tensors.
+
+        :param LabelTensor lt: the tensor to merge.
+        :return: the merged tensors
+        :rtype: LabelTensor
+        """
+        if set(self.labels).intersection(lt.labels):
+            raise RuntimeError('The tensors to merge have common labels')
+
+        new_labels = self.labels + lt.labels
+        new_tensor = torch.cat((self, lt), dim=1)
+        return LabelTensor(new_tensor, new_labels)