use LabelTensor, fix minor, docs

tests/test_label_tensor.py

@@ -59,3 +59,22 @@ def test_extract_order():
     assert new.labels == label_to_extract
     assert new.shape[1] == len(label_to_extract)
     assert torch.all(torch.isclose(expected, new))
+
+
+def test_merge():
+    tensor = LabelTensor(data, labels)
+    tensor_a = tensor.extract('a')
+    tensor_b = tensor.extract('b')
+    tensor_c = tensor.extract('c')
+
+    tensor_bc = tensor_b.append(tensor_c)
+    assert torch.allclose(tensor_bc, tensor.extract(['b', 'c']))
+
+def test_merge():
+    tensor = LabelTensor(data, labels)
+    tensor_a = tensor.extract('a')
+    tensor_b = tensor.extract('b')
+    tensor_c = tensor.extract('c')
+
+    tensor_bb = tensor_b.append(tensor_b)
+    assert torch.allclose(tensor_b, tensor.extract(['b', 'c']))