Python list of dictionaries - adding the dicts with same key names

Question

I have a python list like this:

user = [
        {'name': 'ozzy', 'quantity': 5},
        {'name': 'frank', 'quantity': 4},
        {'name': 'ozzy', 'quantity': 3},
        {'name': 'frank', 'quantity': 2},
        {'name': 'james', 'quantity': 7},
        ]

I am trying to write the code to join the dictionaries with the same name by also adding the quantities. The final list will be that:

user = [
        {'name': 'ozzy', 'quantity': 8},
        {'name': 'frank', 'quantity': 6},
        {'name': 'james', 'quantity': 7}
        ]

I have tried a few things but I am struggling to get the right code. The code I have written below is somewhat adding the values (actually my list is much longer, I have just added a small portion for reference).

newList = []
    quan = 0
    for i in range(0,len(user)):      
        originator = user[i]['name']
        for j in range(i+1,len(user)):
            if originator == user[j]['name']:
                quan = user[i]['quantity'] + user[j]['quantity']
                newList.append({'name': originator, 'Quantity': quan})

can you please help me to get the correct code?

what is the problem with the code you've written? Is the output incorrect? Please give your current and your expected output. — Zinki, Apr 18 '18 at 09:18

score 5 · Answer 1 · answered Apr 18 '18 at 09:20

Just count the items in a collections.Counter, and expand back to list of dicts if needed:

user = [
        {'name': 'ozzy', 'quantity': 5},
        {'name': 'frank', 'quantity': 4},
        {'name': 'ozzy', 'quantity': 3},
        {'name': 'frank', 'quantity': 2},
        {'name': 'james', 'quantity': 7},
        ]

import collections

d = collections.Counter()
for u in user:
    d[u['name']] += u['quantity']

print(dict(d))

newlist = [{'name' : k, 'quantity' : v} for k,v in d.items()]

print(newlist)

outputs Counter dict first, which is already sufficient:

{'frank': 6, 'ozzy': 8, 'james': 7}

and the reformatted output using list of dicts:

[{'name': 'frank', 'quantity': 6}, {'name': 'ozzy', 'quantity': 8}, {'name': 'james', 'quantity': 7}]

sciroccorics · Accepted Answer · 2018-04-18T11:27:46.027

1

The solution is also straightforward with a standard dictionary. No need for Counter or OrderedDict here:

user = [
        {'name': 'ozzy', 'quantity': 5},
        {'name': 'frank', 'quantity': 4},
        {'name': 'ozzy', 'quantity': 3},
        {'name': 'frank', 'quantity': 2},
        {'name': 'james', 'quantity': 7},
        ]

dic = {}
for item in user:
  n, q = item.values()
  dic[n] = dic.get(n,0) + q
print(dic)

user = [{'name':n, 'quantity':q} for n,q in dic.items()]
print(user)

Result:

{'ozzy': 8, 'frank': 6, 'james': 7}
[{'name': 'ozzy', 'quantity': 8}, {'name': 'frank', 'quantity': 6}, {'name': 'james', 'quantity': 7}]

edited Apr 18 '18 at 11:27

answered Apr 18 '18 at 09:37

sciroccorics

2,357
1
8
21

Thanks, this is working good but when I have a key with a blank like 'name surname' then I can not use it withing dict() but instead {'name surname' : k, 'quantity' : v} fixed that part. – Rikkas Apr 18 '18 at 11:24
Good point! As your example didn't show that case, I skipped it. I've edited the answer... – sciroccorics Apr 18 '18 at 11:26

score 0 · Answer 3 · answered Apr 18 '18 at 09:20

I would suggest changing the way the output dictionary looks so that it is actually useable. Consider something like this

user = [
        {'name': 'ozzy', 'quantity': 5},
        {'name': 'frank', 'quantity': 4},
        {'name': 'ozzy', 'quantity': 3},
        {'name': 'frank', 'quantity': 2},
        {'name': 'james', 'quantity': 7},
        ]

data = {}
for i in user:
    print(i)
    if i['name'] in data:
        data[i['name']] += i['quantity']
    else:
        data.update({i['name']: i['quantity']})

print(data)

{'frank': 6, 'james': 7, 'ozzy': 8}

everything in your for loop could be condensed down to a single line using `.get()` - `data[i['name']] = data.get(i['name'], 0) + i['quantity']` - but this still doesn't give OP's desired output — asongtoruin, Apr 18 '18 at 09:31

score 0 · Answer 4 · answered Apr 18 '18 at 09:24

If you need to maintain the original relative order:

from collections import OrderedDict

user = [
        {'name': 'ozzy', 'quantity': 5},
        {'name': 'frank', 'quantity': 4},
        {'name': 'ozzy', 'quantity': 3},
        {'name': 'frank', 'quantity': 2},
        {'name': 'james', 'quantity': 7},
        ]

d = OrderedDict()
for item in user:
    d[item['name']] = d.get(item['name'], 0) + item['quantity']

newlist = [{'name' : k, 'quantity' : v} for k, v in d.items()]
print(newlist)

Output:

[{'name': 'ozzy', 'quantity': 8}, {'name': 'frank', 'quantity': 6}, {'name': 'james', 'quantity': 7}]

score 0 · Answer 5 · answered Apr 18 '18 at 09:36

user = [
    {'name': 'ozzy', 'quantity': 8},
    {'name': 'frank', 'quantity': 6},
    {'name': 'james', 'quantity': 7}
]

reference_dict = {}

for item in user :
    reference_dict[item['name']] = reference_dict.get(item['name'],0) + item['quantity']

#Creating new list from reference dict
updated_user = [{'name' : k , 'quantity' : v} for k,v in reference_dict.items()]

print updated_user

Python list of dictionaries - adding the dicts with same key names

5 Answers5