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Dictionary add values ​​for the same keys

I have a list of dictionaries:

[{'name':'Jay', 'value':'1'},{'name':'roc', 'value':'9'},{'name':'Jay', 'value':'7'},{'name':'roc', 'value':'2'}]

I want this to be:

[{'name':'Jay', 'value':'8'},{'name':'roc', 'value':'11'}]

I have tried scrolling, but I cannot find an example where I can do this. Any hints or ideas would be appreciated.

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7 replies


You can use defaultdict:

lst = [{'name':'Jay', 'value':'1'},{'name':'roc', 'value':'9'},{'name':'Jay', 'value':'7'},{'name':'roc', 'value':'2'}]

1) the values ​​of the sum for each name:

from collections import defaultdict    
result = defaultdict(int)

for d in lst:
    result[d['name']] += int(d['value'])


2) converts a name-value pair to a dictionary in a list:

[{'name': name, 'value': value} for name, value in result.items()]
# [{'name': 'roc', 'value': 11}, {'name': 'Jay', 'value': 8}]

Or, if you want the value as type str commented by @Kevin:

[{'name': name, 'value': str(value)} for name, value in result.items()]
​# [{'name': 'roc', 'value': '11'}, {'name': 'Jay', 'value': '8'}]
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This is a good use case itertools.groupby

.

from itertools import groupby
from operator import itemgetter

orig = [{'name':'Jay', 'value':'1'},
        {'name':'roc', 'value':'9'},
        {'name':'Jay', 'value':'7'},
        {'name':'roc', 'value':'2'}]

get_name = itemgetter('name')
result = [{'name': name, 'value': str(sum(int(d['value']) for d in dicts))}
           for name, dicts in groupby(sorted(orig, key=get_name), key=get_name)]


Destruction:

  • get_name

    is a function that provides a dictionary, returns the value of its "name". Ie, get_name = lambda x: x['name']

    .

  • sorted

    returns a list of dictionaries sorted by key value "name"

    .

  • groupby

    returns an iterator (name, dicts)

    , where dicts

    is a list of (ok, generator) dicts shared name

    as key value "name"

    . (Grouping occurs only for consecutive items with the same key value, so you need to sort the list in the previous step.)

  • The result is a list of new dictionaries using the given name and the sum of all related items "value"

    .

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Similar to Psidom but using collections.Counter

which is an ideal candidate for accumulating integer values.

import collections

d =[{'name':'Jay', 'value':'1'},{'name':'roc', 'value':'9'},{'name':'Jay', 'value':'7'},{'name':'roc', 'value':'2'}]

c = collections.Counter()
for sd in d:
    c[sd["name"]] += int(sd["value"])

Then you need to rebuild the dicts if necessary by converting back to string.

print([{"name":n,"value":str(v)} for n,v in c.items()])

result:

[{'name': 'Jay', 'value': '8'}, {'name': 'roc', 'value': '11'}]
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For completeness, without collections.defaultdict

:

data = [{'name': 'Jay', 'value': '1'}, {'name': 'roc', 'value': '9'},
        {'name': 'Jay', 'value': '7'}, {'name': 'roc', 'value': '2'}]

result = {}
# concetrate
for element in data:
    result[element["name"]] = result.get(element["name"], 0) + int(element["value"])
# unpack
result = [{"name": element, "value": result[element]} for element in result]
# optionally, you can loop through result.items()
# you can, also, turn back result[elements] to str if needed

print(result)
# prints: [{'name': 'Jay', 'value': 8}, {'name': 'roc', 'value': 11}]
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Another way to solve your question is with the groupby

from module itertools

:

from itertools import groupby

a = [{'name':'Jay', 'value':'1'},{'name':'roc', 'value':'9'},{'name':'Jay', 'value':'7'},{'name':'roc', 'value':'2'}]
final = []
for k,v in groupby(sorted(a, key= lambda x: x["name"]), lambda x: x["name"]):
    final.append({"name": k, "value": str(sum(int(j["value"]) for j in list(v)))})

print(final)

Output:

[{'name': 'Jay', 'value': '8'}, {'name': 'roc', 'value': '11'}]
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Here's another way to use pandas

names = [{'name':'Jay', 'value':'1'},{'name':'roc', 'value':'9'},{'name':'Jay', 'value':'7'},
         {'name':'roc', 'value':'2'}]

df = pd.DataFrame(names)
df['value'] = df['value'].astype(int)
group = df.groupby('name')['value'].sum().to_dict()
result = [{'name': name, 'value': value} for name, value in group.items()]

What are the outputs:

[{'value': 8, 'name': 'Jay'}, {'value': 11, 'name': 'roc'}]
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ld = [{'name':'Jay', 'value':'1'},{'name':'roc', 'value':'9'},{'name':'Jay', 'value':'7'},{'name':'roc', 'value':'2'}]

tempDict = {}
finalList = []


for d in ld:
  name = d['name']
  value = d['value']
  if name not in tempDict:
    tempDict[name] = 0
  tempDict[name] += int(value)

#tempDict => {'Jay': 8, 'roc': 11}

for name,value in tempDict.items():
  finalList.append({'name':name,'value':value})
print(finalList)  

# [{'name': 'Jay', 'value': 8}, {'name': 'roc', 'value': 11}]
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