https://blender.stackexchange.com/q/158440/3710

blender-two-dimensional-uilist.py

# ##### BEGIN GPL LICENSE BLOCK #####
#
#  This program is free software; you can redistribute it and/or
#  modify it under the terms of the GNU General Public License
#  as published by the Free Software Foundation; either version 2
#  of the License, or (at your option) any later version.
#
#  This program is distributed in the hope that it will be useful,
#  but WITHOUT ANY WARRANTY; without even the implied warranty of
#  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
#  GNU General Public License for more details.
#
#  You should have received a copy of the GNU General Public License
#  along with this program; if not, write to the Free Software Foundation,
#  Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
#
# ##### END GPL LICENSE BLOCK #####

bl_info = {
    "name": "Two-dimensional UIList",
    "author": "p2or",
    "version": (0, 0, 1),
    "blender": (2, 80, 0),
    "location": "Text Editor > Tools Panel",
    "category": "Development"
}


import bpy

from bpy.props import (IntProperty,
                       BoolProperty,
                       StringProperty,
                       CollectionProperty,
                       PointerProperty)

from bpy.types import (Operator,
                       PropertyGroup,
                       UIList,
                       Panel)


# -------------------------------------------------------------------
#   Properties
# -------------------------------------------------------------------

class CUSTOM_ObjectProps(PropertyGroup):
    #obj_idx: IntProperty()
    obj_ref: PointerProperty(
        name="Object",
        type=bpy.types.Object
        )

class CUSTOM_NameProps(PropertyGroup):
    active_obj_index: IntProperty()
    object_collection: CollectionProperty(
        name = "Object Collection",
        type = CUSTOM_ObjectProps
        )

class CUSTOM_SceneProps(PropertyGroup):
    active_user_index: IntProperty()
    user_collection: CollectionProperty(
        name = "Name Collection",
        type = CUSTOM_NameProps)
                
# -------------------------------------------------------------------
#   Operators
# -------------------------------------------------------------------

class CUSTOM_OT_AddOperator(Operator):
    """Tooltip"""
    bl_idname = "scene.ctm_add_operator"
    bl_label = "Simple Add Operator"

    def execute(self, context):
        scn = context.scene
        custom = scn.ctm
        
        # Clear name collection
        #custom.user_collection.clear()
        
        """ Add user item """
        my_user = custom.user_collection.add()
        
        from random import choice
        my_user.name = choice(("Bob", "Lucy", "John", "Anne", "Sophie"))
                
        """ Add all objects in the scene """
        # Clear object collection
        #my_user.object_collection.clear()
        
        for obj in scn.objects:
            my_obj = my_user.object_collection.add()
            my_obj.name = "{}_{}".format(my_user.name, obj.name)
            my_obj.obj_ref = obj
        
        """ Set active index of both lists to the last item """
        custom.active_user_index = len(custom.user_collection)-1
        my_user.active_obj_index = len(my_user.object_collection)-1
        
        return {'FINISHED'}


class CUSTOM_OT_PrintOperator(Operator):
    """Tooltip"""
    bl_idname = "scene.ctm_print_operator"
    bl_label = "Simple Print Operator"
    
    def execute(self, context):
        scn = context.scene
        custom = scn.ctm
        lookup_dict = {}
        
        """ Print user and attribs """
        for uc, user in enumerate(custom.user_collection):
            print ("User: {}, Name: {}, Ref: {}".format(uc, user.name, user))
            
            """ Print objects and attribs """
            for oc, obj in enumerate(user.object_collection):
                print ("-> Object {}, Ref {}".format(oc, obj))
                lookup_dict.setdefault(user, []).append(obj.obj_ref)
        
        """ In case, dicts are nice """
        print ("\nLookup:", lookup_dict)
        return {'FINISHED'}


class CUSTOM_OT_ClearOperator(Operator):
    """Tooltip"""
    bl_idname = "scene.ctm_clear_operator"
    bl_label = "Simple Clear Operator"
    
    remove_all: BoolProperty(options={'SKIP_SAVE'})
    
    def execute(self, context):
        custom = context.scene.ctm
        
        for uc in custom.user_collection:
            uc.object_collection.clear()
            uc.active_obj_index = -1
        
        if self.remove_all: 
            custom.user_collection.clear()
            custom.active_user_index = -1
            
        return {'FINISHED'}


# -------------------------------------------------------------------
#   Draw
# -------------------------------------------------------------------

class CUSTOM_UL_Main(UIList):
    
    def draw_item(self, context, layout, data, item, icon, active_data, active_propname, index):
        layout.row().prop(item, "name", text="{}".format(index), emboss=False, translate=False, icon="USER")
            
    def invoke(self, context, event):
        pass   

class CUSTOM_UL_Sub(UIList):
    def draw_item(self, context, layout, data, item, icon, active_data, active_propname, index):
        split = layout.split(factor=0.6)
        custom_icon = "OUTLINER_OB_{}".format(item.obj_ref.type)
        split.prop(item.obj_ref, "name", text="{}".format(index), emboss=False, translate=False, icon=custom_icon)
        split.label(text="User: {}".format(data.name))
            
    def invoke(self, context, event):
        pass
    

class CUSTOM_PT_ObjectList(Panel):
    """Adds a custom panel to the TEXT_EDITOR"""
    bl_idname = 'TEXT_PT_my_panel'
    bl_space_type = "TEXT_EDITOR"
    bl_region_type = "UI"
    bl_label = "Multi-dimensional UIList"

    def draw(self, context):
        layout = self.layout
        scn = context.scene
        custom = scn.ctm
        
        min_rows = 10
        draw_fac = 0
        user = None
        
        row = layout.row()
        split = layout.split(factor=draw_fac)
        
        split.template_list(
            listtype_name = "CUSTOM_UL_Main", 
            list_id  = "", 
            dataptr = custom, 
            propname = "user_collection", 
            active_dataptr = custom, 
            active_propname = "active_user_index",
            rows = min_rows
            )
        
        if len(custom.user_collection) > 0 and \
            custom.active_user_index != -1:
            
            draw_fac = 0.5
            user = custom.user_collection[custom.active_user_index]
                
            split.template_list(
                listtype_name = "CUSTOM_UL_Sub",
                list_id = "", 
                dataptr = user,
                propname = "object_collection",
                active_dataptr = user,
                active_propname = "active_obj_index",
                rows = min_rows
                )

        layout.row().operator(CUSTOM_OT_PrintOperator.bl_idname, text="Print to Console", icon="CONSOLE")
        
        row = layout.row()
        row.operator(CUSTOM_OT_ClearOperator.bl_idname, text="Remove Users", icon="REMOVE").remove_all = True
        row.operator(CUSTOM_OT_ClearOperator.bl_idname, text="Remove Objects", icon="REMOVE")
        
        layout.row().operator(CUSTOM_OT_AddOperator.bl_idname, text="Add User Entry", icon="USER")
        if user and user.active_obj_index >= 0:
            obj = user.object_collection[user.active_obj_index]    
            layout.label(text="Selection: {} | {}".format(user.name, obj.obj_ref.name))
            

# -------------------------------------------------------------------
#   Register & Unregister
# -------------------------------------------------------------------

classes = (
    CUSTOM_ObjectProps,
    CUSTOM_NameProps,
    CUSTOM_SceneProps,
    CUSTOM_OT_AddOperator,
    CUSTOM_OT_PrintOperator,
    CUSTOM_OT_ClearOperator,
    CUSTOM_UL_Main,
    CUSTOM_UL_Sub,
    CUSTOM_PT_ObjectList
)

def register():
    from bpy.utils import register_class
    for cls in classes:
        register_class(cls)
    
    bpy.types.Scene.ctm = PointerProperty(type=CUSTOM_SceneProps)    

def unregister():
    from bpy.utils import unregister_class
    for cls in reversed(classes):
        unregister_class(cls)
    
    del bpy.types.Scene.ctm


if __name__ == "__main__":
    register()