duplicating values in a certain way inside a list inside a dictionary

Question

I am new to programming as well as python, and I have a question that I have not found an answer for on the internet. I was wondering if any of you geniuses will be able to help me out.

I have a dictionary and in the dictionary, the keys are strings and the values are lists. I was wondering if it was possible to turn this dictionary:

dict1 = {'a':(1, 4, 7), 'b':(2, 5, 8), 'c':(3, 6, 9)}

have each value duplicated once into this format so the duplicates are next to the originals:

dict1 = {'a':(1, 1, 4, 4, 7, 7), 'b':(2, 2, 5, 5, 8, 8), 'c':(3, 3, 6, 6, 9, 9)}

Answer 1

You can use a dictionary comprehension :

>>> dict1 = {'a':(1, 4, 7), 'b':(2, 5, 8), 'c':(3, 6, 9)}
>>> {x:tuple(z for z in y for _ in xrange(2)) for x,y in dict1.iteritems()}
{'a': (1, 1, 4, 4, 7, 7), 'c': (3, 3, 6, 6, 9, 9), 'b': (2, 2, 5, 5, 8, 8)}
>>>

Note however that the above code was built in Python 2.7. If you are on Python 3.x, you will want this:

>>> dict1 = {'a':(1, 4, 7), 'b':(2, 5, 8), 'c':(3, 6, 9)}
>>> {x:tuple(z for z in y for _ in range(2)) for x,y in dict1.items()}
{'a': (1, 1, 4, 4, 7, 7), 'c': (3, 3, 6, 6, 9, 9), 'b': (2, 2, 5, 5, 8, 8)}
>>>

Also, in both solutions, the order of the keys cannot be guaranteed. That is just a result of the way dictionaries are implemented in Python.

Answer 2

Firstly, your values are tuples, not lists. The difference is subtle, but the relevant part is that tuples are not mutable

So, let's first transform what you have to a list-valued dictionary, and then solve your problem

>>> dict1 = {'a':(1, 4, 7), 'b':(2, 5, 8), 'c':(3, 6, 9)}
>>> dict1 = {k:list(v) for k,v in dict1.items()}
>>> dict1
{'b': [2, 5, 8], 'c': [3, 6, 9], 'a': [1, 4, 7]}
>>> answer = {k:list(itertools.chain.from_iterable(zip(v,v))) for k,v in dict1.items()}
>>> answer
{'b': [2, 2, 5, 5, 8, 8], 'c': [3, 3, 6, 6, 9, 9], 'a': [1, 1, 4, 4, 7, 7]}