Dynamic nested dictionary using Python

Question

I have a dataframe like this:

from    to
B       C
A       B
D       E
D       F
B       D

I want to create a nested dictionary than contains from and to values. The final output will look like this:

{ "A": {
          "B": {
                   "C":
                   "D": {
                           "E": {},
                           "F": {},
                        }
               }
         }
}

 

My code is:

d = dict()
curr = d
for p, c in [("B", "C"), ("A", "B"), ("D", "E"), ("D", "F"), ("B", "D")]:
    
    # First time
    if not d:
        d.setdefault(p, {}).setdefault(c, {})
    
    # Check if p is a parent
    if p in d:
        curr = curr.setdefault(p, {}).setdefault(c, {})
        
    else:
        if c in d:
            curr = d
            curr.setdefault(p, {}).setdefault(c, d.get(c))
            del d[c]
        else:
            curr = d
            for k, v in curr.items():
                if p in v:
                    curr = v
                    curr.setdefault(p, {}).setdefault(c, {})
            else:
                curr.setdefault(p, {}).setdefault(c, {})

The result is:

{'A': {'B': {'C': {}}},
 'B': {'D': {'E': {},
             'F': {}}}}

I don't know how to check whether one key is already a parent or a child and substitute if it's already a child/parent

Answer 1

How about this

pairs = [("B", "C"), ("A", "B"), ("D", "E"), ("D", "F"), ("B", "D")]

d = {}
for a, b in pairs:
    d.setdefault(a, {})[b] = d.setdefault(b, {})

ok = {'A': d['A']}
print(ok)

prints

{'A': {'B': {'C': {}, 'D': {'E': {}, 'F': {}}}}}

Here is version that is a bit more dynamic and supports multiple top level keys.

import json

pairs = [
    ("B", "C"),
    ("A", "B"),
    ("D", "E"),
    ("D", "F"),
    ("B", "D"),
    ("z", "x")
]

d = {}
something_points_to = set()
for a, b in pairs:
    something_points_to.add(b)
    d.setdefault(a, {})[b] = d.setdefault(b, {})

root_keys = [key for key in d if key not in something_points_to]
final_result = {key: d[key] for key in root_keys}


print(json.dumps(final_result, indent=4))

That should give you:

{
    "A": {
        "B": {
            "C": {},
            "D": {
                "E": {},
                "F": {}
            }
        }
    },
    "z": {
        "x": {}
    }
}