Find the max value in list of dictionaries and return keys

Question

I have I have such a datastructure:

   dataset = [{'country': 'Afghanistan',
     'continent': 'Asia',
     '1990': 500,
     '1991': 500,
     '1992': 500,
     '1993': 1000},
    {'country': 'Albania',
    'continent': 'Europe',
    '1990': 100,
    '1991': 100,
    '1992': 100,
    '1993': 100}
    {'country': 'Algeria',
    'continent': 'Africa',
    '1990': 500,
    '1991': 500,
    '1992': 1000,
    '1993': 1000
    }]

I need to find max value in year 1991 and create a dictionary with keys - country, where this maximum value was, the year we are looking for (1991) and the maximum value found.

I was thinking of making it that way, but it didn't work.

    new_dict = {}
    str_year = str(year)
    for dict_ in dataset:
        for key, values in dict_.items():
        max_val = max(dict_, key=lambda x:x[str_year])
        new_dict = {'country' : dict_['country'], 'year': year, 'cases': max_val}
     return new_dict

How can I do this?

https://stackoverflow.com/questions/18296755/python-max-function-using-key-and-lambda-expression — barker, Oct 02 '21 at 14:29

score 2 · Accepted Answer · answered Oct 02 '21 at 14:26

You don't need to iterate through the list of dictionaries - max() will give you the one you want to work with. Then you just need to extract the correct fields, like this:

max_val = max(dataset, key=lambda x:x[str_year])
new_dict = {'country' : max_val['country'], 'year': year, 'cases': max_val[str_year]}

(Also note that your definition of dataset was syntaxtically incorrect)

{'country': 'Albania',
    'continent': 'Europe',
    '1990': 100,
    '1991': 100,
    '1992': 100,
    '1993': 100},
               ^^   missing the close of the dictionary

KiranM · Answer 2 · 2021-10-02T14:43:10.183

You can do in both ways:

Directly using max(lambda):

>>> max_dict = max(dataset, key=lambda x: x["1991"])
>>> new_dict = {'country':max_dict['country'], 'year':'1991', 'cases':max_dict['1991']}
>>> new_dict
{'country': 'Afghanistan', 'year': '1991', 'cases': 500}
>>>

Using manual looping:

>>> max_cntry=""
>>> max_1991=0
>>> for itm in dataset:
...     if itm['1991'] > max_1991:
...         max_1991 = itm['1991']
...         max_cntry = itm['country']
... 
>>> new_dict={'country':max_cntry, 'year':1991, 'cases':max_1991}
>>> print(new_dict)
{'country': 'Afghanistan', 'year': 1991, 'cases': 500}
>>>

You might need to handle appropriately if there is a match. There are 2 matches in sample dataset.

Find the max value in list of dictionaries and return keys

2 Answers2