From BlenderWiki

Misc Editing Tools

Here are regrouped some “odd” mesh editing tools, of seldom use – all of them share one common point: they do not alter the shape of your mesh.

ObData To Center

This tool shifts the whole mesh data, to re-center it on the object’s center. Even though it tastes and smells like the same option in Object mode, it has a different result, as here it is the barycenter of the vertices that is computed – which have as effect that the “center” of the mesh will be computed near heavily dense parts of the mesh (in Object mode, it is the barycenter of the faces that is computed, I think – anyway, the result seems more “natural”!).

Vertex List Ordering

The Mesh Tools panel (Editing context) has two buttons that modify the order of the selected vertices in the vertex-list of the mesh. This is a geek thing – I’m not even sure it is of any use, but, as they exist, let’s describe them anyway…

Hash

This will randomly reorder (!) the selected vertices in the mesh vertex list.

Xsort

This will reorder the selected vertices in the mesh vertex list, using their X-coordinate (in which space? View? Local?) as sort key. Might be useful to speed up a bit the OpenGL rendering (for Blender display or Game Engine framerate).

Face List Ordering

As well as the vertex list order, you can reorganize the face list order. This can have its importance, e.g. when using the Build modifier.

This is only available in Object mode (as well as “painting” modes), don’t ask me why… This implies that unlike vertices, it will always affects all faces of a mesh.

The only way to sort the faces seems to be the Sort Faces pop-up menu, appearing when you press the CtrlF keys (you’ll note it’s the same shortcut as the one showing the Face Special menu, in Edit mode…).

Note also that face sorting isn’t recorded in the global undo/redo system!

Options

As the menu states it itself, for all options described below, you can inverse the sort order by holding the Ctrl key while clicking on the one you want.

View Axis

Sorts the faces using their position along the current viewing axis (if you have multiple 3D views, it is the axis of the one from where you called the menu). By default, the sort is done from back to front, hold Ctrl while clicking to inverse it. Use the Camera view (0 NumPad) to sort the faces according to their distance from the camera!

Cursor Distance

Sorts the faces using their distance to the 3D cursor. Here again, the sort is done by default from the most far faces to the nearest ones, use Ctrl to inverse this.

Material

Sorts the faces using their material index, from the lowest to the highest by default (as usual, use Ctrl to inverse this). Note that this is a “partial” sort (unless each face has a different material index…), i.e. the relative order of the faces sharing a same material index is preserved…

Selection

Well, I don’t really know what this option does exactly… Sometimes it alters the current order, sometimes not…

Randomize

Randomizes the order of the faces in the list! Note that using Ctrl it a bit meaningless here, as by definition, randomness has no order…