python中的分组字典键值
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Group dictionary key values in python
提问by Alchemist777
I have the following dictionary
我有以下字典
mylist = [{'tpdt': '0.00', 'tmst': 45.0, 'tmdt': 45.0, 'pbc': 30, 'remarks': False, 'shift': 1, 'ebct': '0.00', 'tmcdt': '0.00', 'mc_no': 'KA20'},
{'tpdt': '0.00', 'tmst': 45.0, 'tmdt': 45.0, 'pbc': 30, 'remarks': False, 'shift': 1, 'ebct': '0.00', 'tmcdt': '0.00', 'mc_no': 'KA20'},
{'tpdt': '0.00', 'tmst': 55.0, 'tmdt': 55.0, 'pbc': 30, 'remarks': False, 'shift': 1, 'ebct': '0.00', 'tmcdt': '0.00', 'mc_no': 'KA23'},
{'tpdt': '0.00', 'tmst': 55.0, 'tmdt': 55.0, 'pbc': 30, 'remarks': False, 'shift': 1, 'ebct': '0.00', 'tmcdt': '0.00', 'mc_no': 'KA23'}]
I want to get the sum of the key 'tmst' for every dictionary values 'KA20' and 'KA23' in the list of dictionaries.
我想获得字典列表中每个字典值 'KA20' 和 'KA23' 的键 'tmst' 的总和。
Could you please have your suggestions on this??
请问您对此有什么建议吗？？
采纳答案by alecxe
You can use itertools.groupby:
您可以使用itertools.groupby：
>>> for key, group in itertools.groupby(mylist, lambda item: item["mc_no"]):
... print key, sum([item["tmst"] for item in group])
...
KA20 90.0
KA23 110.0
Note that for groupbyto work properly, mylisthas to be sorted by the grouping key:
请注意，为了groupby正常工作，mylist必须按分组键排序：
from operator import itemgetter
mylist.sort(key=itemgetter("mc_no"))
回答by Milan Thakkar
First you needs to sort that list of dictionaries..using following code.. Ex.
首先，您需要对字典列表进行排序..使用以下代码..例如。
animals = [{'name':'cow', 'size':'large'},{'name':'bird', 'size':'small'},{'name':'fish', 'size':'small'},{'name':'rabbit', 'size':'medium'},{'name':'pony', 'size':'large'},{'name':'squirrel', 'size':'medium'},{'name':'fox', 'size':'medium'}]
import itertools
from operator import itemgetter
sorted_animals = sorted(animals, key=itemgetter('size'))
then you use following code
然后你使用以下代码
for key, group in itertools.groupby(sorted_animals, key=lambda x:x['size']):
print key,
print list(group)
After you will get following result...
得到以下结果后...
large [{'name': 'cow', 'size': 'large'}, {'name': 'pony', 'size':'large'}]
medium [{'name': 'rabbit', 'size': 'medium'}, {'name': 'squirrel', 'size':'medium'}, {'name': 'fox', 'size': 'medium'}]
small [{'name': 'bird', 'size': 'small'}, {'name': 'fish', 'size': 'small'}]
回答by jfs
Here's a code that doesn't require mylistto be sorted by "mc_no"key:
这是一个不需要按键mylist排序的代码"mc_no"：
from collections import defaultdict
sums = defaultdict(int) # key -> sum
for d in mylist:
sums[d["mc_no"]] += d["tmst"]
