Merging two dictionaries where items are interchanged-CodePudding

Assume I've got the dictionaries:

dict1 = {'A': 1, 'B': 2, 'C' : 3}
dict2 = {'a': 4, 'b': 5, 'c' : 6}

This link suggest several ways to merge the two but all of the merges are simply concatenations. I want to merge them like a dealer shuffles cards, or like a zipper zips. What I mean by this is that once merging dict1 and dict2, the resulting dict3 should become

dict3 = {'A': 1, 'a': 4, 'B': 2, 'b': 5, 'C' : 3, 'c' : 6}

So the merge grabs elements from dict1 and dict2 in an alternating fashion. My dictionaries are in fact very large so doing it manually is not an option.

CodePudding user response：

There is round-robin itertools recipe to select data this way.

You can use:

dict3 = dict(roundrobin(dict1.items(), dict2.items()))

output:

{'A': 1, 'a': 4, 'B': 2, 'b': 5, 'C': 3, 'c': 6}

recipe:

from itertools import cycle, islice
def roundrobin(*iterables):
    "roundrobin('ABC', 'D', 'EF') --> A D E B F C"
    # Recipe credited to George Sakkis
    num_active = len(iterables)
    nexts = cycle(iter(it).__next__ for it in iterables)
    while num_active:
        try:
            for next in nexts:
                yield next()
        except StopIteration:
            # Remove the iterator we just exhausted from the cycle.
            num_active -= 1
            nexts = cycle(islice(nexts, num_active))

You can also use more-itertools.interleave

from more_itertools import interleave

dict(interleave(dict1.items(), dict2.items()))

CodePudding user response：

Indented for readability:

from itertools import chain
dict(
    chain.from_iterable(
        zip(dict1.items(), dict2.items())
    )
)

If your dictionaries are not guaranteed to be of equal size, adapt this solution to use itertools.zip_longest() instead of basic zip()

CodePudding user response：

There are many things that could go wrong with this approach. What if your 2 dictionnaries don't have the same length? What if they have duplicate keys? What if later you need 3 dicts instead of 2?

Also, do you have a real use case behind this requirement? Do you really need to build a new dict with all data like this, or do you simply need to iterate over the (key, value) pairs in a specific, alternate fashion like this?

Assuming you don't have to worry about the above, if you only need to iterate, you could simply do something like that:

def iter_zip(dict1, dict2):
    for i1, i2 in zip(dict1.items(), dict2.items()):
        yield i1
        yield i2
   
dict1 = {'A': 1, 'B': 2, 'C' : 3}
dict2 = {'a': 4, 'b': 5, 'c' : 6}

# you can then do
for key, val in iter_zip(dict1, dict2):
    do_something(key, val)

And if you really need to build a new dict, it is now as simple as:

dict(iter_zip(dict1, dict2))
# {'A': 1, 'a': 4, 'B': 2, 'b': 5, 'C': 3, 'c': 6}