将多个值添加到字典键

Question

I have two lists:

list1 = ['670', '619', '524', '670', '693', '693', '693', '632', '671']
list2 = ['JAIPUR', 'MUMBAI', 'DELHI', 'UDAIPUR', 'GOA', 'GOA', 'GOA', 'LUCKNOW', 'JAIPUR']

I want to make a dictionary out of this. Please note the two lists exactly in the order that it should be mapped into. Like for key '670' value us 'JAIPUR' and so on.

But when I tried, it gives output as:

d = dict(zip(list1, list2))

{'670': 'UDAIPUR', '619': 'MUMBAI', '524': 'DELHI', '693': 'GOA', '632': 'LUCKNOW', '671': 'JAIPUR'}

It takes only the latest value if multiple values are found for a single key. However what I want is multiple values for a single key like 670 should have:

'670': ['JAIPUR', 'UDAIPUR']

Can anyone help.

Answer 1

Use defaultdict :

>>> from collections import defaultdict
>>> d = defaultdict(list)
>>> for i,key in enumerate(list1): 
        if list2[i] not in d[key]:            #to add only unique values (ex: '693':'goa')
            d[key].append(list2[i]) 

>>> d
=> defaultdict(<class 'list'>, {'670': ['JAIPUR', 'UDAIPUR'], '619': ['MUMBAI'], 
               '524': ['DELHI'], '693': ['GOA'], '632': ['LUCKNOW'], '671': ['JAIPUR']})

Answer 2

What you need is grouping by the list1 items. Use collections.defaultdict object:

import collections

list1 = ['670', '619', '524', '670', '693', '693', '693', '632', '671']
list2 = ['JAIPUR', 'MUMBAI', 'DELHI', 'UDAIPUR', 'GOA', 'GOA', 'GOA', 'LUCKNOW', 'JAIPUR']
result = collections.defaultdict(list)

for t in zip(list1, list2):
    result[t[0]].append(t[1])

print(dict(result))

The output:

{'524': ['DELHI'], '671': ['JAIPUR'], '632': ['LUCKNOW'], '670': ['JAIPUR', 'UDAIPUR'], '619': ['MUMBAI'], '693': ['GOA', 'GOA', 'GOA']}

Answer 3

Since dicts can not have more than one element with the same key the newer values for that key that are assigned to a dict overwrite the older ones.

So with this code it works:

list1 = ['670', '619', '524', '670', '693', '693', '693', '632', '671']
list2 = ['JAIPUR', 'MUMBAI', 'DELHI', 'UDAIPUR', 'GOA', 'GOA', 'GOA', 'LUCKNOW', 'JAIPUR']

def extendDictValue(d, key, value):
    if key in d:
        d[key].append(value)
    else:
        d[key] = [value]

d={}
for key, value in zip(list1, list2):
    extendDictValue(d, key, value)

print(d)