在列表的不同字典中添加相同键的值

Question

I have a list of dictionaries:

my_list = [
{"Name": "John Doe", "Amount": 150},
{"Name": "Peter Doe", "Amount": 40},
{"Name": "Peter Doe", "Amount": 10},
{"Name": "Lisa Doe", "Amount": 90},
{"Name": "John Doe", "Amount": 200},]

I want to iterate through the list of dictionaries and find the same values for the key "Name" if the values are the same, I want to add the "Amounts" and save it to a new dictionary. For example, the list above should become:

my_list_2 = [
{"Name": "John Doe", "Amount": 350},
{"Name": "Peter Doe", "Amount": 50},
{"Name": "Lisa Doe", "Amount": 90},]

Would anyone please suggest any Pythonic ways of doing it?

Thanks a lot!

Answer 1

Would you be open to use dataframe to accomplish this?

my_list = [
{"Name": "John Doe", "Amount": 150},
{"Name": "Peter Doe", "Amount": 40},
{"Name": "Peter Doe", "Amount": 10},
{"Name": "Lisa Doe", "Amount": 90},
{"Name": "John Doe", "Amount": 200}]
df = pd.DataFrame(my_list)
display(df.groupby('Name').sum())

Output

            Amount
    Name    
John Doe    350
Lisa Doe    90
Peter Doe   50

Or you could do some dictionary manipulation:

new_dict = {}
for e in my_list:
    if e['Name'] not in new_dict.keys():
        new_dict[e['Name']] = e['Amount']
    else:
        new_dict[e['Name']] += e['Amount']

my_list_2 = []
for k,v in new_dict.items():
    my_list_2.append({'Name': k, 'Amount': v})
my_list_2

Output my_list_2 is

[{'Name': 'John Doe', 'Amount': 350},
 {'Name': 'Peter Doe', 'Amount': 50},
 {'Name': 'Lisa Doe', 'Amount': 90}]

Edit: Thank you @Nk03, to get the same output

my_list_2 = df.groupby('Name' , as_index=False).sum().to_dict('records')

Answer 2

You can use itertools groupby :

from itertools import groupby
my_list_2 = [{'Name': g, 'Amount': sum(i['Amount'] for i in k)} for g, k in groupby(
    sorted(my_list, key=lambda x: x['Name']), key=lambda x: x['Name'])]

OUTPUT :

[{'Name': 'John Doe', 'Amount': 350},
 {'Name': 'Lisa Doe', 'Amount': 90},
 {'Name': 'Peter Doe', 'Amount': 50}]

Answer 3

Since you only want a sum for each name, I'd suggest a slightly different data structure for my_list_2 :

my_list_2 = {}
for entry in my_list:
    name = entry["Name"]
    amount = entry["Amount"]
    my_list_2.setdefault(name, 0)
    my_list_2[name] += amount

This iterates your original list entry by entry and cheks if the name is already known. If not, it sets it's sum to 0. Finally, the amount of the current entry is added to the current sum. In the end, you get a dict that looks like this:

{'John Doe': 350, 'Peter Doe': 50, 'Lisa Doe': 90}

If you really want your old structure back, you can re-transform it using some list comprehension magic:

my_list_3 = [{"Name": name, "Amount": amount} for name, amount in my_list_2.items()]

However, if you have other data attached to your dicts, you might need to re-fetch it from your original list later.