CODEWITHSUNDEEP
pythonjsondictionaryrecursionformatting
tijmenvanetten
tijmenvanetten

Reputation: 111

Creating nested dictionary from list of tuples

Given a list called outlines containing tuples: (level, title), create a nested dictionary with depth based on the level and key value based on the title.

Example list:
[(1, Abstract)
(2, Background)
(2, Methods)
(2, Results)
(3, Statistics)
(3, Images)
(1, Introduction)]

This should output:

{
"Abstract": {
    "Background": {}, 
    "Methods": {}, 
    "Results": {
        "Statistics": {},
        "Images": {}
    }
},
"Introduction": {}
}

So far I've tried a recursive solution but so far has resulted in untraceable erroneous behavior. This is the best solution I've come up with so far, but I have trouble preventing duplicates in different levels due to the predefined for-loop:

def structure(outlines, current_level=1, previous_title=''):
    section = dict()
    for i, (level, title) in enumerate(outlines):
        if level == current_level:
            section[title] = {}
            previous_title = title
        elif level > current_level:
            section[previous_title] = structure(outlines[i:], level)
        elif level < current_level:
            pass # Unknown
    return section

Any tips?

Upvotes: 0

Views: 367

Answers (3)

Mark Saving
Mark Saving

Reputation: 1797

We already have a working solution thanks to John R. Paul, but I wanted a solution which doesn't rely on dictionaries being ordered. As an added bonus, the solution is non-recursive (although John R. Paul's solution is tail-recursive and thus can be trivially rewritten to use a while loop).

def add_all(generator_of_pairs):
    stack = [{}]
    for (level, name) in generator_of_pairs:
        del stack[level:]
        new_dict = {}
        stack[level - 1][name] = new_dict
        stack.append(new_dict)
    return stack[0]

Note that this solution assumes that nesting levels cannot increase by more than 1 from 1 element to the next - but hopefully it should be obvious that this assumption is necessary.

Upvotes: 1

John Paul R
John Paul R

Reputation: 752

This is my recursive solution:

import json
inlist = [
    (1, "Abstract"),
    (2, "Background"),
    (2, "Methods"),
    (2, "Results"),
    (3, "Statistics"),
    (3, "Images"),
    (1, "Introduction"),
]

out = dict()
# IMPORTANT: Dictionaries are ordered in Python 3.6 (under the CPython implementation at least) unlike in previous incarnations.
def addElem(dest_level, new_elem, current_container, current_level=1):
    # list(current_container.keys())[-1] gets the most recently added element at the current level.
    if (current_level < dest_level):
        addElem(dest_level, new_elem, current_container[list(current_container.keys())[-1]], current_level+1)
    else:
        current_container[new_elem] = dict()

for el in inlist:
    addElem(el[0], el[1], out)

print(json.dumps(out, indent=2))

Output:

{
  "Abstract": {
    "Background": {},
    "Methods": {},
    "Results": {
      "Statistics": {},
      "Images": {}
    }
  },
  "Introduction": {}
}

Upvotes: 0

Matt
Matt

Reputation: 1294

Assuming that the order matters then this would work:

generator = [
    (1, 'Abstract'),
    (2, 'Background'),
    (2, 'Methods'),
    (2, 'Results'),
    (3, 'Statistics'),
    (3, 'Images'),
    (1, 'Introduction')
]

# keep track of latest place in the dict
current_tree = []

# dict that you want to generate
d = {}

for i, value in generator:

    # if this, then you are at the highest level
    # so just add your value at the top
    if current_tree==[] or i==1:
        d[value] = {}
        current_tree = [value]

    # otherwise go back in the tree and add your value
    else:

        tmp_d = d
        for key in current_tree[:i-1]:
            tmp_d = tmp_d[key]

        tmp_d[value] = {}

        current_tree = current_tree[:i] + [value]

This returns:

{'Abstract': {'Background': {'Images': {}, 'Statistics': {}},
              'Methods': {},
              'Results': {}},
 'Introduction': {}}

Upvotes: 0

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