python - Sum of dict elements

Question

I have a dictionary of names and ages. Some of the names are identical. I want to sum the age of the names that are identical.

My fake data looks like this:

pete: 33
ann: 7
ruth: 3
ann: 5
austin: 90

In the examples there are two anns. So I want to sum the ages of the two anns. Currently I have a dictionary:

dict = {'pete':33,'ann':7,'ruth':3,'ann':5,'austin':90}

My result should look like this

dict = {'pete':33,'ann':12,'ruth':3,'austin':90}

pete: 33
ann: 12
ruth: 3
austin: 90

I think to put the data in a dictionary like this isn't the best solution. What is a good other solution to store the data and process them into the output?

Answer 1

你的假数据不可能是那样的。字典中不可能有两个具有相同键的条目，也许您打算使用不同的数据结构？（不是字典）。但是，如果您的数据如下所示：

input = [('pete', 33), ('ann',7), ('ruth',3), ('ann',5), ('austin',90)]

那么adefaultdict将是一个好主意：

from collections import defaultdict
d = defaultdict(int)

for k, v in input:
    d[k] += v

d
=> defaultdict(<type 'int'>, {'pete': 33, 'ann': 12, 'ruth': 3, 'austin': 90})

或使用Counter：

from collections import Counter
d = Counter()

for k, v in input:
    d.update({k:v})

d
=> Counter({'austin': 90, 'pete': 33, 'ann': 12, 'ruth': 3})

还有另一个解决方案，无需导入额外的库：

d = {}
for k, v in input:
    if k in d:
        d[k] += v
    else:
        d[k] = v

d
=> {'pete': 33, 'ann': 12, 'ruth': 3, 'austin': 90}

Answer 2

data = [('pete', 33), ('ann', 7), ('ruth', 3), ('ann', 5), ('austin', 90)]

由于 dicts 不能包含重复的键，因此您可以从元组列表开始。

from collections import defaultdict
combined = defaultdict(int)

for name, age in data:
    combined[name] += age

然后构建dict使用defaultdict. 诀窍是defaultdict(int)创建一个字典，其条目默认为 0，因此您不必处理不存在的键。

Answer 3

您需要使用元组列表，而不是使用字典

pairs = [ ('pete', 33), ('ann', 7), ('ruth', 3), ('ann', 5), ('austin', 90) ]

然后您可以使用 defaultdict 计算总和：

from collections import defaultdict
answer = defaultdict(int)
for name, number in pairs:
    answer[name] += number

print(answer)

defaultdict 通过调用给定函数 (int) 来为任何不存在的键提供默认值（int() 方便地返回 0）；然后对于每次迭代，将数字添加到其中。