json list to nested based on id

How would I group JSON objects by id’s to make a nested JSON in Python? The JSON is structured this way:

  [{
    "id": "4",
    "title": "Part  4",
    "children": {}
  },{
    "id": "4.1.",
    "title": "Section  4.1.  Transition Rule",
    "children": {}
  },
  {
    "id": "4.1.1.",
    "title": "4.1.1.  Transition, January 2014",
    "children": {}
  },
  {
    "id": "4.1.1.1.",
    "title": "4.1.1.1.  Transition Rule",
    "children": {}
  },
  {
    "id": "4.1.2.",
    "title": "4.1.2.  Transition, January 2015",
    "children": {}
  },
  {
    "id": "4.1.2.1.",
    "title": "4.1.2.1.  Transition Rule",
    "children": {}
  },
]]

The goal is to have a tree structure where each object(section) contains all its subsections going from 4 to 4.1 > 4.1.1 > 4.1.1.1.
The snippet of the required output is below:

[
   {
      "id":"4",
      "title":"Part  4",
      "children":{
         {
            "id":"4.1.",
            "title":"Section  4.1.  Transition Rule",
            "children":{
               {
                  "id":"4.1.1.",
                  "title":"4.1.1.  Transition, January 2014",
                  "children":{
                     {
                        "id":"4.1.1.1.",
                        "title":"4.1.1.1.  Transition Rule",
                        "children":{
                           
                        }
                     }
                  }
               },
               {
                  "id":"4.1.2.",
                  "title":"4.1.2.  Transition, January 2015",
                  "children":{
                     {
                        "id":"4.1.2.1.",
                        "title":"4.1.2.1.  Transition Rule",
                        "children":{
                           
                       

Answer

You can use recursion:

from collections import defaultdict
def get_tree(d):
  _d, r = defaultdict(list), []
  for i in d:
     _d[i['key'][0]].append({**i, 'key':i['key'][1:]})
  for b in _d.values():
     j, k = [l for l in b if not l['key']], [l for l in b if l['key']]        
     if j:
        r.extend([{**{x:y for x, y in i.items() if x != 'key'}, 'children':get_tree(k)} for i in j])
     else:
        r.extend(get_tree(k))
  return r
  

data = [{'id': '4', 'title': 'Part  4', 'children': {}}, {'id': '4.1.', 'title': 'Section  4.1.  Transition Rule', 'children': {}}, {'id': '4.1.1.', 'title': '4.1.1.  Transition, January 2014', 'children': {}}, {'id': '4.1.1.1.', 'title': '4.1.1.1.  Transition Rule', 'children': {}}, {'id': '4.1.2.', 'title': '4.1.2.  Transition, January 2015', 'children': {}}, {'id': '4.1.2.1.', 'title': '4.1.2.1.  Transition Rule', 'children': {}}, {'id': '4.1.3.', 'title': '4.1.3.  Transition, January 2017', 'children': {}}]

---

import json
print(json.dumps(get_tree([{**i, 'key':[*filter(None, i['id'].split('.'))]} for i in data]), indent=4))

Output:

[
  {
    "id": "4",
    "title": "Part  4",
    "children": [
        {
            "id": "4.1.",
            "title": "Section  4.1.  Transition Rule",
            "children": [
                {
                    "id": "4.1.1.",
                    "title": "4.1.1.  Transition, January 2014",
                    "children": [
                        {
                            "id": "4.1.1.1.",
                            "title": "4.1.1.1.  Transition Rule",
                            "children": []
                        }
                    ]
                },
                {
                    "id": "4.1.2.",
                    "title": "4.1.2.  Transition, January 2015",
                    "children": [
                        {
                            "id": "4.1.2.1.",
                            "title": "4.1.2.1.  Transition Rule",
                            "children": []
                        }
                    ]
                },
                {
                    "id": "4.1.3.",
                    "title": "4.1.3.  Transition, January 2017",
                    "children": []
                 }
             ]
          }
       ]
   }
]