Recursive sums in dictionary

Question

i've got a classic tree problem and can't find the right solution. I have a tree represented in a python dictionary with branches and leafes. I need to calculate the sum of all children (price-property) for every branch and store it in the sum-property. Here is a sample of my tree (dict):

[
    {
        "id": 1,
        "type": "group",
        "name": "test-group 1",
        "price": 0,
        "sum": 0,
        "children": [
            {
                "id": 2,
                "type": "position",
                "name": "test-inner 1",
                "price": 5
            },
            {
                "id": 3,
                "type": "position",
                "name": "test-inner 2",
                "price": 10
            }
        ]
    },
    {
        "id": 4,
        "type": "group",
        "name": "test-group 2",
        "sum": 0,
        "children": [
            {
                "id": 5,
                "type": "position",
                "name": "test-inner 3",
                "price": 5
            },
            {
                "id": 6,
                "type": "group",
                "name": "test-group 3",
                "sum": 0,
                "children": [
                    {
                        "id": 7,
                        "type": "position",
                        "name": "test-inner 4",
                        "price": 5
                    },
                    {
                        "id": 8,
                        "type": "position",
                        "name": "test-inner 5",
                        "price": 10
                    }
                ]
            }
        ]
    }
]

I'm sure i need recursion and already found solutions to get the sum of the whole tree...but i need the partial sums too...

Thanks for your help!

Are non-leaf nodes supposed to have prices, like the first one does? The second tree doesn't. — Personman, Feb 12 '18 at 16:26

Personman · Answer 1 · 2018-02-13T16:25:08.947

0

Assuming that non-leaf nodes don't have prices, this does it:

def add_sums(tree):
  if 'price' in tree:
    return tree['price']
  s = sum(map(add_sums, tree['children']))
  tree['sum'] = s
  return s

If they do need to be able to have prices, as possibly indicated by your test data, then you can do

def add_sums(tree):
  if 'children' not in tree:
      return tree['price']
  s = sum(map(add_sums, tree['children']))
  if 'price' in tree:
     s += tree['price']
  tree['sum'] = s
  return s

possibly moving the addition of the node price to after updating the sum, if it's supposed to be only the sum of the children.

edited Feb 13 '18 at 16:25

answered Feb 12 '18 at 16:30

Personman

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Should work as well...but there is a little typo with the function name in the map call... – Creaticious Feb 13 '18 at 07:20
thanks, fixed! also, the 15-char minimum on comments is really stupid! – Personman Feb 13 '18 at 16:25

score 0 · Accepted Answer · answered Feb 12 '18 at 16:31

You can try somtehing along the following lines:

def dct_sum(dct):
    if isinstance(dct, dict):
        if 'price' in dct:
            return dct['price']
        if 'children' in dct:
            dct['sum'] = sum(dct_sum(c) for c in dct['children'])
            return dct['sum']
    if isinstance(dct, list):
        return sum(dct_sum(item) for item in dct)
    return 0

Recursive sums in dictionary

2 Answers2