CODEWITHSUNDEEP
python
Luke B
Luke B

Reputation: 1194

Aggregate values by using Counter

Is there a way to aggregate the value of each entry of a list using Counter, and not just count the number of time an entry is present ?

For example, if I have a list

from collections import Counter

lst = [
    ['John', 1],
    ['James', 2],
    ['John', 3],
    ['Andy', 1]
]

and I do

total = Counter(name for name, num in lst)
print(total)

The output will be

Counter({'John': 2, 'James': 1, 'Andy': 1})

Which is expected. I was just wondering if there's a way to obtain

Counter({'John': 4, 'James': 2, 'Andy': 1})

I know there are many ways to do it, but I'm looking for a way to do it with Counter.

Upvotes: 2

Views: 166

Answers (3)

JarroVGIT
JarroVGIT

Reputation: 5324

You need to loop through the list and update the counter accordingly.

c = Counter()

for k, v in lst:
    c.update({k: v})

>>> print(c)
Counter({'John': 4, 'James': 2, 'Andy': 1})

You can also use a list comprehension, but using a comprehension for side effects is not recommended:

[c.update({k: v}) for k, v in lst]
print(c)

Output is the same.

Upvotes: 2

wjandrea
wjandrea

Reputation: 33007

You can use a simple loop to add the values:

total = Counter()
for name, num in lst:
    total[name] += num

print(total)  # -> Counter({'John': 4, 'James': 2, 'Andy': 1})

If there's a way to do this in one line in O(n), I'd love to know.

Upvotes: 2

DarrylG
DarrylG

Reputation: 17156

Adding another level of for loop to posted list comprehension

total = Counter(name for name, num in lst for _ in range(num))

print(total)
# Output: Counter({'John': 4, 'James': 2, 'Andy': 1})

Upvotes: 2

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