How to merge around 300+ duplicate materials?

Question

I just made a scene with a city made of mostly identical skyscrapers. I did that by copying and pasting. Then I joined all of them with Ctrl+J, but now I can't undo the join and I have got around 300+ glass and wall materials in one obj. My question is how do I merge them into 1 glass and 1 wall material so I can change all windows and all walls at once? Selecting them all is not an option. I have 1000+ windows in my scene and now in one obj.

Short version: I mucked up and now I need to clean up 300+ materials. How can I do that? Maybe an add-on?

edit: I tried deleting all but the first glass and wall. i had one skyscraper left that had colors.

edit2: my materials are in alternating order. like glass, wall, glass, wall, glass, wall.... i think you get the idea.

Answer 1

The following script extends from the already linked answer in that it removes any double-materials and assigns the 'correct' materials to the faces respectively. However, you'll need to understand that a few assumptions are made here:

• your original material is named something
• the duplicates are named something.045, something.046 and so on
• they are REALLY duplicates
• you've saved your scene before you run this :)
• the active object in your scene is the mesh object you want to clean

Copy the following Python code to a text editor within your file and run it:

import bpy

# only search on own object materials
mat_list = [x.material.name for x in bpy.context.object.material_slots]
remove_slots = []


# the following only works in object mode
bpy.ops.object.mode_set(mode='OBJECT')

for s in bpy.context.object.material_slots:
    if s.material.name[-3:].isnumeric():
        # the last 3 characters are numbers
        # that indicates it might be a duplicate of another material
        # but this is pure guesswork, so expect errors to happen!
        if s.material.name[:-4] in mat_list:

            # there is a material without the numeric extension so use it
            # this again is just guessing that we're having identical node trees here

            # get the material index of the 'clean' material
            index_clean = mat_list.index(s.material.name[:-4])
            index_wrong = mat_list.index(s.material.name)
            print(index_wrong, index_clean)

            # get the faces which are assigned to the 'wrong' material
            faces = [x for x in bpy.context.object.data.polygons if x.material_index == index_wrong]

            for f in faces:
                f.material_index = index_clean

            remove_slots.append(s.name)

# now remove all empty material slots:
for s in remove_slots:

    if s in [x.name for x in bpy.context.object.material_slots]:
        print('removing slot %s' % s)
        bpy.context.object.active_material_index = [x.material.name for x in bpy.context.object.material_slots].index(s)
        bpy.ops.object.material_slot_remove()

It should turn this:

into this:

Answer 2

If you enter edit mode, you can select each glass material, and click select (Not sure if you can select all of them, and click select once or do them individually off the top of my head) then once everything that uses all of your glass materials is selected, delete all but one of them with the minus button near the top of the panel, then select that one material and click the "Assign" button underneath the panel. Rinse and repeat for the walls.