sort a nested list of dicts by key in python

January 23, 2022

Below is an example nested list of dictionaries. I want to order the lists by the number of points that Charlie has.

l = [[{'Name': 'Alice',   'Age': 40, 'Point': 80},
      {'Name': 'Bob',     'Age': 20             },
      {'Name': 'Charlie', 'Age': 30, 'Point': 10}],
     [{'Name': 'Alice',   'Age': 40, 'Point': 80},
      {'Name': 'Bob',     'Age': 20             },
      {'Name': 'Charlie', 'Age': 30, 'Point': 30}],
     [{'Name': 'Alice',   'Age': 40, 'Point': 80},
      {'Name': 'Bob',     'Age': 20             },
      {'Name': 'Charlie', 'Age': 30, 'Point': 20}]]

The output should look like this.

l = [[{'Name': 'Alice',   'Age': 40, 'Point': 80},
      {'Name': 'Bob',     'Age': 20             },
      {'Name': 'Charlie', 'Age': 30, 'Point': 10}],
     [{'Name': 'Alice',   'Age': 40, 'Point': 80},
      {'Name': 'Bob',     'Age': 20             },
      {'Name': 'Charlie', 'Age': 30, 'Point': 20}],
     [{'Name': 'Alice',   'Age': 40, 'Point': 80},
      {'Name': 'Bob',     'Age': 20             },
      {'Name': 'Charlie', 'Age': 30, 'Point': 30}]]

I think I should be able to use sorted() with the right arguments, but I’m not sure what the syntax would be.

sorted(l, key=lambda x: x[ ????? ])

Charlie is always the third item in the sublists.

>Solution :

If Charlie is always third, you could use this:

sorted(l, key=lambda x: x[2]['Point'])

Otherwise, you’d want to use a helper function:

def get_charlie_points(lst):
    for item in lst:
        if item['Name'] == 'Charlie':
            return item['Point']
    return 0  # Replace this with the number you want if there is no Charlie, or raise an exception

sorted(l, key=get_charlie_points)