创建每个键具有多个值的字典

Question

How can I create a dictionary with multiple values per key from 2 lists?

For example, I have:

>>> list1 = ['fruit', 'fruit', 'vegetable']

>>> list2 = ['apple', 'banana', 'carrot']

And, I want something to the effect of:

>>> dictionary = {'fruit': ['apple', 'banana'], 'vegetable': ['carrot']}

I have tried the following so far:

>>> keys = list1
>>> values = list2
>>> dictionary = dict(zip(keys, values))
>>> dictionary
    {'fruit': 'banana', 'vegetable': 'carrot'}

Answer 1

You can use dict.setdefault and a simple for-loop:

>>> list1 = ["fruit", "fruit", "vegetable"]
>>> list2 = ["apple", "banana", "carrot"]
>>> dct = {}
>>> for i, j in zip(list1, list2):
...     dct.setdefault(i, []).append(j)
... 
>>> dct
{'fruit': ['apple', 'banana'], 'vegetable': ['carrot']}

From the docs :

setdefault(key[, default])

If key is in the dictionary, return its value. If not, insert key with a value of default and return default . default defaults to None .

Answer 2

You can use collections.defaultdict for such tasks :

>>> from collections import defaultdict
>>> d=defaultdict(list)
>>> for i,j in zip(list1,list2):
...    d[i].append(j)
... 
>>> d
defaultdict(<type 'list'>, {'vegetable': ['carrot'], 'fruit': ['apple', 'banana']})

Answer 3

This is a bit different from the other answers. It is a bit simpler for beginners.

list1 = ['fruit', 'fruit', 'vegetable']
list2 = ['apple', 'banana', 'carrot']
dictionary = {}

for i in list1:
    dictionary[i] = []

for i in range(0,len(list1)):
    dictionary[list1[i]].append(list2[i])

It will return

{'vegetable': ['carrot'], 'fruit': ['apple', 'banana']}

This code runs through list1 and makes each item in it a key for an empty list in dictionary . It then goes from 0-2 and appends each item in list2 to its appropriate category, so that index 0 in each match up, index 1 in each match up, and index 2 in each match up.