Python 2.7: 2 lists with duplicate value into a dictionary

Question

If I have 2 lists:

fruits = ["apple","apple","oranges","watermelon","apple"]
val = ["a","b","c","d","e"]

Each index of val corresponds to the index of fruits

So if I want a dictionary with:

dict
{
"apple" : ["a","b","e"],
"oranges": ["c"],
"watermelon": ["d"]
}

What is the simplest way to achieve this?

@scharette I think they meant for that to be a dictionary with list values — Edward Minnix, Aug 02 '18 at 18:39
Even though the mechanic is the same, I'm not sure if that's an exact duplicate though. — scharette, Aug 02 '18 at 18:43

score 4 · Answer 1 · answered Aug 02 '18 at 18:39

Use a defaultdict with list factory as the output container and iterate over the two lists with zip:

In [162]: out = collections.defaultdict(list)

In [163]: for k, v in zip(fruits, val):
     ...:     out[k].append(v)
     ...:     

In [164]: out
Out[164]: 
defaultdict(list,
            {'apple': ['a', 'b', 'e'], 'oranges': ['c'], 'watermelon': ['d']})

In [165]: dict(out)
Out[165]: {'apple': ['a', 'b', 'e'], 'oranges': ['c'], 'watermelon': ['d']}

score 0 · Answer 2 · answered Aug 02 '18 at 18:39

You can use setdefault to initilize each value with an empty list, then append the values from the other list

fruits = ["apple","apple","oranges","watermelon","apple"]
val = ["a","b","c","d","e"]
d={}

for k, v in zip(fruits, val):
    d.setdefault(k, []).append(v) 

print(d)
# {'apple': ['a', 'b', 'e'], 'oranges': ['c'], 'watermelon': ['d']}

Python 2.7: 2 lists with duplicate value into a dictionary

2 Answers2