Sum nested lists based on condition in Python

Question

I have a nested list looking like this:

[[\'Vienna\',\'2012\', 890,503,70],[\'London\',\'2014\', 5400, 879,78],
 [\'London\',\'2014\',4800,70,90],[\'Bern\',\'201         


        

Answer 1

You can achieve the result you want by simply using a dictionary store all the country names and years as one value. Each key in the dictionary is a tuple of the country name and the corresponding year.

Ex: key = (country,year).

This allows us to have the unique values that we need to group them by.

L = [
        ['Vienna','2012', 890,503,70],['London','2014', 5400, 879,78],
        ['London','2014',4800,70,90],['Bern','2013',300,450,678],
        ['Vienna','2013', 700,850,90], ['Bern','2013',500,700,90]
    ]

    countries = {}

    for list in L:
        key = tuple(list[0:2])
        values = list[2:]
        if key in countries:
            countries[key] = [sum(v) for v in zip(countries[key],values)]
        else:
            countries[key] = values

    print(countries)

out:

 {
     ('Vienna', '2012'): [890, 503, 70],
     ('London', '2014'): [10200, 949, 168],
     ('Bern', '2013'): [800, 1150, 768],
     ('Vienna', '2013'): [700, 850, 90]
}