user59046 user59046 - 2 months ago 4
Python Question

Create dictionary from multi-dimensional list without duplicating keys

I'd like to take a list of tuples with multiple elements and turn it into a multi-dimensional dictionary without repeating keys. So if the following is my original list:

myList = [('jeep', 'red', 2002, 4), ('jeep', 'red', 2003, 6), ('jeep', 'blue', 2003, 4), ('bmw', 'black', 2015, 8)]


I would want to take the above and turn it into a dictionary in this format:

{'jeep':
{'red': [
[2002, 4],
[2003, 6]]
'blue': [
[2003, 4]]
},
'bmw':
{'black': [
[2015, 8]]
}
}


I seemed to be on the right path with Python's defaultdict, but I can't seem to completely solve this. Thanks!

Answer

Using a lot of dict.setdefault...

myList = [('jeep', 'red', 2002, 4), ('jeep', 'red', 2003, 6), ('jeep', 'blue', 2003, 4), ('bmw', 'black', 2015, 8)]

d = {}
for model, colour, year, month in myList:
    d.setdefault(model, {}).setdefault(colour, []).append([year, month])

For each item in myList, either get the current dictionary for the model or create the key with a new empty dict, then with that dict, either retrieve the list for that colour, or set the key with a new empty list, then append the year and month as a 2-element list to that list...

Gives you d:

{'bmw': {'black': [[2015, 8]]},
 'jeep': {'blue': [[2003, 4]], 'red': [[2002, 4], [2003, 6]]}}
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