通过将两个字典的值合并到排序列表中来合并两个字典

Question

I'm having trouble writing a function union_collections that consumes two dictionaries (d1 and d2) representing two book collections. The function produces a new dictionary containing all books present in d1 or d2, while maintaining the following rules:

• The produced dictionary should not contain any duplicate book titles.
• Each list of book titles within the produced dictionary should be sorted using the built- in sort() method.
• CANNOT use the built-in function fromkeys() in solution

These are sample collections for testing:

collection1 = \
         {'f':['flatland', 'five minute mysteries', 'films of the 1990s', 'fight club'],
         't':['the art of computer programming', 'the catcher in the rye'],
         'p':['paradise lost', 'professional blackjack', 'paradise regained'],
         'c':['calculus in the real world', 'calculus revisited', 'cooking for one'],
         'd':['dancing with cats', 'disaster at midnight']}

collection2 = \
        {'f':['flatland', 'films of the 1990s'],
         'a':['a brief history of time', 'a tale of two cities'],
         'd':['dealing with stress', 'dancing with cats'],
         't':['the art of computer programming', 'the catcher in the rye'],
         'p':['power and wealth', 'poker essentials', 'post secret'],
         'c':['cat couples', 'calculus', 'calculus revisited',
              'cooking for one', 'calculus in the real world', 'cooking made easy']}`

An example: unique_collections(collection1, collection2) should produce:

{'f' : ['fight club' , 'films of the 1990s', 'five minute mysteries', 'flatland'],
 't' : ['the art of computer programming', 'the catcher in the rye'],
 'p' : ['paradise lost' , 'paradise regained', 'poker essentials', 'post secret' , 'power and wealth', 'professional blackjack'],
 'c' : ['calculus' , 'calculus in the real world' , 'calculus revisited' , 'cat couples', 'cooking for one', 'cooking made easy'],
 'd' : ['dancing with cats' , 'dealing with stress' , 'disaster at midnight'],
 'a' : ['a brief history of time' , 'a tale of two cities']}`

So far I've written:

def union_collections(d1, d2):
    union = {}

    for key in d1 or d2:
        if key in d1 and key not in d2: # if the key is only in d1
            union[key] = d1[val]

        if key in d2 and key not in d1: #
            union[key] = d2[val]

        if key in d1 and key in d2:
            union = dict(list(d1.items()) + list(d2.items()))

    return sorted(union.values())

This function isn't working and I have no idea how to fix it to adhere to the following requirements.

CANNOT import any modules.

Answer 1

def union_collections(d1, d2):
    return { k: sorted(list(set(d1.get(k, []) + d2.get(k, []))))
             for k in set(d1.keys() + d2.keys()) }

Same as above, but attempting to be more readable:

def union_collections(d1, d2):
    return { k: sorted(
                    list(
                        set(
                            d1.get(k, []) + d2.get(k, [])
                        )
                    )
                )
             for k in set(d1.keys() + d2.keys()) }

Output:

{'a': ['a brief history of time', 'a tale of two cities'],
 'c': ['calculus',
       'calculus in the real world',
       'calculus revisited',
       'cat couples',
       'cooking for one',
       'cooking made easy'],
 'd': ['dancing with cats', 'dealing with stress', 'disaster at midnight'],
 'f': ['fight club',
       'films of the 1990s',
       'five minute mysteries',
       'flatland'],
 'p': ['paradise lost',
       'paradise regained',
       'poker essentials',
       'post secret',
       'power and wealth',
       'professional blackjack'],
 't': ['the art of computer programming', 'the catcher in the rye']}

Answer 2

Some issues in your code -

1. When you do - union = dict(list(d1.items()) + list(d2.items())) - Do not think this is valid, you cannot add dictionaries. And do not need to as well, this does not make sense for your requirement.

2. sorted() returns the sorted list, it does not do in place sorting. And this would just return the sorted list of values , not the dictionary, you need to use list.sort() or sorted() function when creating the dictionaries directly.

3. for key in d1 or d2 - this only iterates over the keys in d1, you need to use set(d1.keys()).union(d2.keys()) .

4. d1[val] ( d2[val] ) - is not correct, there is not val variable, use d1[key] instead.

For the case where a key is found in both dictionary, you can add the lists of both dictionaries and then convert it to set and back to list and then sort it and then assign it back to the union dictionary. Example -

def union_collections(d1, d2):
    union = {}

    for key in set(d1.keys()).union(d2.keys()):
        if key in d1 and key not in d2: # if the key is only in d1
            union[key] = d1[key]

        if key in d2 and key not in d1: 
            union[key] = d2[key]

        if key in d1 and key in d2:
            union[key] = sorted(list(set(d1[key] + d2[key])))

    return union

---

As it was asked in the comments -

for when a key is in both dictionaries, is there a way to do this without the use of sets?

The way to do it without sets would be -

def union_collections(d1, d2):
    union = {}

    for key in set(d1.keys()).union(d2.keys()):
        if key in d1 and key not in d2: # if the key is only in d1
            union[key] = d1[key]

        if key in d2 and key not in d1: 
            union[key] = d2[key]

        if key in d1 and key in d2:
            y = []
            union[key] = y
            for x in d1[key]:
                y.append(x)
            for x in d2[key]:
                if x not in y:
                    y.append(x)
            y.sort()

    return union