add test for split and fix off by one bug.

fsl_mrs/tests/test_utils_nifti_mrs_tools_split_merge.py

@@ -364,7 +364,7 @@ def test_split():
 
     # Functionality testing
 
-    out_1, out_2 = nmrs_tools.split(nmrs, 'DIM_DYN', 32)
+    out_1, out_2 = nmrs_tools.split(nmrs, 'DIM_DYN', 31)
     assert out_1.data.shape == (1, 1, 1, 4096, 32, 32)
     assert out_2.data.shape == (1, 1, 1, 4096, 32, 32)
     assert np.allclose(out_1.data, nmrs.data[:, :, :, :, :, 0:32])
@@ -382,6 +382,21 @@ def test_split():
     assert np.allclose(out_1.data, nmrs.data[:, :, :, :, :, test_list])
     assert np.allclose(out_2.data, nmrs.data[:, :, :, :, :, [0, 32, 63]])
 
+    # Split some synthetic data with header information
+    nhdr_1 = gen_new_nifti_mrs(np.ones((1, 1, 1, 10, 4), dtype=complex),
+                               1 / 1000,
+                               100,
+                               '1H',
+                               dim_tags=['DIM_DYN', None, None])
+
+    nhdr_1.set_dim_header('DIM_DYN', {'RepetitionTime': [1, 2, 3, 4]})
+
+    out_1, out_2 = nmrs_tools.split(nhdr_1, 'DIM_DYN', 1)
+    assert out_1.shape == (1, 1, 1, 10, 2)
+    assert out_1.hdr_ext['dim_5'] == 'DIM_DYN'
+    assert out_1.hdr_ext['dim_5_header'] == {'RepetitionTime': [1, 2]}
+    assert out_2.hdr_ext['dim_5_header'] == {'RepetitionTime': [3, 4]}
+
 
 def test_merge():
     """Test the merge functionality

fsl_mrs/utils/nifti_mrs_tools/split_merge.py

@@ -56,7 +56,7 @@ def split(nmrs, dimension, index_or_indicies):
                 or index_or_indicies >= nmrs.shape[dim_index]:
             raise ValueError('index_or_indicies must be between 0 and N-1,'
                              f' where N is the size of the specified dimension ({nmrs.shape[dim_index]}).')
-        index = np.arange(index_or_indicies, nmrs.shape[dim_index])
+        index = np.arange(index_or_indicies + 1, nmrs.shape[dim_index])
 
     elif isinstance(index_or_indicies, list):
         if not np.logical_and(np.asarray(index_or_indicies) >= 0,