Create a json tree from csv list in python

Question

I'm trying to build a json hierarchy from a simple table in python.

The data comes in looking like the following:

id         parent          name
1          10              test-name-1
2          10              test-name-2
3          5               test-name-3
4          none            test-name-4
5          10              test-name-5
6          none            test-name-6
7          1               test-name-7
8          1               test-name-8
9          8               test-name-9
10         4               test-name-10

and I'm looking for an output like this:

{"$4":{"name":"test-name-4","children":{
      "$10":{"name":"test-name-10","children":{
            "$1":{"name":"test-name-1","children":{
                 "$7":{"name":"test-name-7","children":{}},
                 "$8":{"name":"test-name-8","children":{
                      "$9":{"name":"test-name-9","children":{}}}}}},
            "$2":{"name":"test-name-2","children":{}},
            "$5":{"name":"test-name-5","children":{
                 "$3":{"name":"test-name-3","children":{}}}}}}}},
 "$6":{"name":"test-name-6","children":"test-name-6"}}

I have no idea how many "leaves" there will be or "roots", or what order the rows from the csv will come in. My question is, is there a way that I can recursively build a dictionary/list from a child node up to the parent? How can I produce a hierarchical tree from the "leaf" pieces of the tree in python?

Thanks for the help!

Not so tough. Create tree nodes for each row (you can keep them in a dictionary using id as key), then add the children to their respective parents. Printing the tree in json should also be simple enough. Just give it a try, and there are many people to help you! — Sufian Latif
– Sufian Latif, Commented Sep 27, 2012 at 8:57

Emmanuel · Accepted Answer · 2012-09-27 14:50:15Z

I have a solution based on 2 loops too (1 to cache, 1 to build), without JSON encoder, and that gives exactly the output you required:

>>> import re
>>> from collections import defaultdict
>>> parents = defaultdict(list)
>>> for i, line in enumerate(file_.split('\n')):
    if i != 0 and line.strip():
        id_, parent, name = re.findall(r'[\d\w-]+', line)
        parents[parent].append((id_, name))


>>> parents
defaultdict(<type 'list'>, {'10': [('1', 'test-name-1'), ('2', 'test-name-2'), ('5', 'test-name-5')], 'none': [('4', 'test-name-4'), ('6', 'test-name-6')], '1': [('7', 'test-name-7'), ('8', 'test-name-8')], '5': [('3', 'test-name-3')], '4': [('10', 'test-name-10')], '8': [('9', 'test-name-9')]})

OK, now we have our cache, the recursive function easily builds the output we'd like:

>>> def build_tree(d, val):
    return {'$' + id_: {'name': name, 'children': build_tree(d, id_)} for id_, name in d[val]}

We just have to call it on the dict built previously, with value 'none' which is the tree root:

>>> from pprint import pprint
>>> pprint(build_tree(parents, 'none'))
{'$4': {'children': {'$10': {'children': {'$1': {'children': {'$7': {'children': {},
                                                                     'name': 'test-name-7'},
                                                              '$8': {'children': {'$9': {'children': {},
                                                                                         'name': 'test-name-9'}},
                                                                     'name': 'test-name-8'}},
                                                 'name': 'test-name-1'},
                                          '$2': {'children': {},
                                                 'name': 'test-name-2'},
                                          '$5': {'children': {'$3': {'children': {},
                                                                     'name': 'test-name-3'}},
                                                 'name': 'test-name-5'}},
                             'name': 'test-name-10'}},
        'name': 'test-name-4'},
 '$6': {'children': {}, 'name': 'test-name-6'}}
>>>

I really wish stack overflow would let me choose more then one answer, as this is also a viable answer to my original question. Thank you for another way of doing it!

score 3 · Accepted Answer · 2012-09-27 09:10:24Z

To assign all child nodes to its parent, you can do two passes over the list of nodes. The first pass adds each node to a UserDict. In the second pass the parent of each node is guaranteed to be in the UserDict so the node can be added to the children of its parent.

To serialize to JSON a JSONEncoder can be used.

#!/usr/bin/env python

import sys
import json
import UserDict

class Node(object):
    def __init__(self, nid, parent, name):
        self.nid = nid
        self.parent = parent
        self.children = []
        self.name = name

class NodeDict(UserDict.UserDict):
    def addNodes(self, nodes):
        """ Add every node as a child to its parent by doing two passes."""
        for i in (1, 2):
            for node in nodes:
                self.data[node.nid] = node
                if node.parent in self.data.keys():
                    if node.parent != "none" and
                       node not in self.data[node.parent].children:
                        self.data[node.parent].children.append(node)

class NodeJSONEncoder(json.JSONEncoder):
    def default(self, node):
        if type(node) == Node:
            return {"nid":node.nid, "name":node.name, "children":node.children}
        raise TypeError("{} is not an instance of Node".format(node))

if __name__ == "__main__":
    nodes = []

    with open(sys.argv[1]) as f:
        for row in f.readlines()[1:]:
            nid, parent, name = row.split()
            nodes.append(Node(nid, parent, name))

    nodeDict = NodeDict()
    nodeDict.addNodes(nodes)

    rootNodes = [node for nid, node in nodeDict.items()
                 if node.parent == "none"]
    for rootNode in rootNodes:
        print NodeJSONEncoder().encode(rootNode)

Result:

{"name": "test-name-4", "nid": "4", "children":[
     {"name": "test-name-10", "nid": "10", "children":[
         {"name": "test-name-1", "nid": "1", "children":[
            {"name": "test-name-7", "nid": "7", "children": []},
            {"name": "test-name-8", "nid": "8", "children":[
                {"name": "test-name-9", "nid": "9", "children": []}]}]},
         {"name": "test-name-2", "nid": "2", "children": []},
         {"name": "test-name-5", "nid": "5", "children":[
             {"name": "test-name-3", "nid": "3", "children": []}]}]}]}
{"name": "test-name-6", "nid": "6", "children": []}

johnaco · Accepted Answer · 2017-10-06 04:27:42Z

The answer given did not work for me in python 3.6 because Dict.Dict has been deprecated. So I made some changes to make it work and generalized it a little by letting user specify columns for child_id, parent_id and child name via command line. Please see below (I am just learning and am sure this could be improved, but it works for my purposes).

""" Converts a CSV file with Parent/Child Hierarchy to a hierarchical JSON file for front-end processing (javascript/DS)

USAGE: csv2json.py <somefile.csv> a b c  (column nrs of a=child_id, b=parent-id, c=name(of child))

ROOT of hierarchy should contain child_id and parent_id = 'none' or blank.  name must exist """

import sys
import json
import csv
#import UserDict
from collections import UserDict

class Node(object):
    def __init__(self, child_id, parent_id, name):
        self.child_id = child_id
        self.parent_id = parent_id
        self.children = []
        self.name = name

class NodeDict(UserDict):
    def addNodes(self, nodes):
        """ Add every node as a child to its parent_id by doing two passes."""
        for i in (1, 2):
            for node in nodes:
                self.data[node.child_id] = node
                if node.parent_id in self.data.keys():
                    if (node.parent_id != "none" or node.parent_id != "") and node not in self.data[node.parent_id].children:
                        self.data[node.parent_id].children.append(node)

class NodeJSONEncoder(json.JSONEncoder):
    def default(self, node):
        if type(node) == Node:
            return {"name":node.name, "children":node.children}
            raise TypeError("{} is not an instance of Node".format(node))

if __name__ == "__main__":
    nodes = []

    with open(sys.argv[1], 'r') as f:
        reader = csv.reader(f)
        for row in reader:
            if not row[int(sys.argv[4])] : #skip if no name/label exists
                continue
            child_id, parent_id, name = row[int(sys.argv[2])] , row[int(sys.argv[3])] , row[int(sys.argv[4])]

            nodes.append(Node(child_id, parent_id, name))

    nodeDict = NodeDict()
    nodeDict.addNodes(nodes)

    rootNodes = [node for child_id, node in nodeDict.items()
                 if (node.parent_id == "none" or node.parent_id == "")]
    for rootNode in rootNodes:
        print(NodeJSONEncoder().encode(rootNode))

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