Python 在 for 循环中将值附加到字典
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appending values to dictionary in for loop
提问by Krishna Chaitanya
Just cant get this working. Any help is highly appreciated.
只是不能得到这个工作。任何帮助都受到高度赞赏。
dict = {}
for n in n1:
if # condition #
dict[key] = []
dict[key].append(value)
print dict
This is printing something like this
这是打印这样的东西
{'k1':['v1']} and {'k1':['v2']}
{'k1':['v1']} 和 {'k1':['v2']}
I have few other nested for loops down this code, which will be using this dict and the dict has only the latest key value pairs i.e. {'k1':'v2'}
我在这段代码中几乎没有其他嵌套的 for 循环，它们将使用这个 dict 并且该 dict 只有最新的键值对，即 {'k1':'v2'}
I am looking for something like {'k1':['v1','v2']}
我正在寻找类似的东西 {'k1':['v1','v2']}
Please suggest a solution without using setdefault
请提出一个不使用的解决方案 setdefault
回答by gzc
You can also check key existence before assign.
您还可以在分配之前检查密钥是否存在。
dict = {}
for n in n1:
if # condition #
if key not in dict:
dict[key] = []
dict[key].append(value)
print dict
回答by Back2Basics
Give collections.defaultdicta try:
#example below is in the docs.
from collections import defaultdict
s = [('yellow', 1), ('blue', 2), ('yellow', 3), ('blue', 4), ('red', 1)]
d = defaultdict(list)
for k, v in s:
d[k].append(v)
print(sorted(d.items()))
[('blue', [2, 4]), ('red', [1]), ('yellow', [1, 3])]
the d = defaultdict(list)line is setting the keys values to be an empty dictionary by default and appending the value to the list in the loop.
该d = defaultdict(list)行默认将键值设置为空字典，并将值附加到循环中的列表中。
回答by deepika
The problem with the code is it creates an empty list for 'key' each time the for loop runs. You need just one improvement in the code:
代码的问题是每次 for 循环运行时它都会为“key”创建一个空列表。您只需要对代码进行一项改进：
dict = {}
dict[key] = []
for n in n1:
if # condition #
dict[key].append(value)
print dict
回答by PRASAD
a=[['a',1],['b',2],['c',1],['a',2],['b',3],['a',3]]
d={}
for i in a:
print (i)
if i[0] not in d:
d[i[0]]= [i[1]]
else:
d[i[0]].append(i[1])
print (d)
OP : {'a': [1, 2, 3], 'b': [2, 3], 'c': [1]}
