Python | Convert a list of lists into tree-like dict
Given a list of lists, write a Python program to convert the given list of lists into a tree-like dictionary.
Examples:
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Input : [[1], [2, 1], [3, 1], [4, 2, 1], [5, 2, 1], [6, 3, 1], [7, 3, 1]]
Output : {1: {2: {4: {}, 5: {}}, 3: {6: {}, 7: {}}}}
Input : [['A'], ['B', 'A'], ['C', 'A'], ['D', 'C', 'A']]
Output : {'A': {'C': {'D': {}}, 'B': {}}}
Method #1 : Naive Method
This is a Naive approach in which we use two for loops to traverse the list of lists. We initialize the empty dictionary ‘tree’ to currTree and each time we check if the key (list of list’s item) is included in the currTree or not. If not, include it in the currTree, otherwise do nothing. Finally, assign the currTree[key] to currTree.
# Python3 program to Convert a list# of lists into Dictionary (Tree form) def formTree(list): tree = {} for item in list: currTree = tree for key in item[::-1]: if key not in currTree: currTree[key] = {} currTree = currTree[key] return tree # Driver Codelst = [['A'], ['B', 'A'], ['C', 'A'], ['D', 'C', 'A']]print(formTree(lst)) |
{'A': {'B': {}, 'C': {'D': {}}}}
Method #2 : Using reduce()
The reduce() function is used to apply a particular function passed in its argument to all of the list elements mentioned in the sequence passed along. We will use reduce() to traverse the dictionary and reuse getTree() to find the location to store the value for setTree(). All but the last element in mapList is needed to find the ‘parent’ dictionary to add the value to, then use the last element to set the value to the right key.
# Python3 program to Convert a list# of lists into Dictionary (Tree form) from functools import reducefrom operator import getitem def getTree(tree, mappings): return reduce(getitem, mappings, tree) def setTree(tree, mappings): getTree(tree, mappings[:-1])[mappings[-1]] = dict() # Driver Codelst = [['A'], ['B', 'A'], ['C', 'A'], ['D', 'C', 'A']]tree ={}for item in lst: setTree(tree, item[::-1]) print(tree) |
{'A': {'B': {}, 'C': {'D': {}}}}
