ENH: Handle new axes in Minc

Author: effigies

nibabel/minc1.py

@@ -325,6 +325,42 @@ def _spatial_dims(self):
             return slice(1, 4)
         return slice(0, 3)
 
+    def _check_slicing(self, slicer, return_spatial=False):
+        ''' Canonicalize slicers and check for scalar indices in spatial dims
+
+        Parameters
+        ----------
+        slicer : object
+            something that can be used to slice an array as in
+            ``arr[sliceobj]``
+        return_spatial : bool
+            return only slices along spatial dimensions (x, y, z)
+
+        Returns
+        -------
+        slicer : object
+            Validated slicer object that will slice image's `dataobj`
+            without collapsing spatial dimensions
+        '''
+        try:
+            all_slices = super(Minc1Image, self)._check_slicing(slicer, False)
+            sp_dims = self._spatial_dims
+        except IndexError:
+            # Prepending a new axis for 3D images is valid in Minc
+            if slicer[0] is None and self._spatial_dims == slice(0, 3):
+                all_slices = (None,) + super(Minc1Image, self)._check_slicing(slicer[1:], False)
+                sp_dims = slice(1, 4)
+            else:
+                raise
+        # Added complications of first axis being time
+        if self._spatial_dims == slice(1, 4) and all_slices[0] is None:
+            raise IndexError("New temporal axis is not permitted in 4D Minc images")
+        elif (self._spatial_dims == slice(0, 3) and len(all_slices) > 3 and
+              all_slices[0] is not None):
+            raise IndexError("New axes cannot be added to 3D Minc image "
+                             "without new temporal axis (first dimension)")
+        return all_slices[sp_dims] if return_spatial else all_slices
+
 
 load = Minc1Image.load