如何在python中减少元组列表 [英] How to reduce on a list of tuples in python
问题描述
我有一个数组,我想计算数组中每个项目的出现.
I have an array and I want to count the occurrence of each item in the array.
我设法使用了map函数来生成元组列表.
I have managed to use a map function to produce a list of tuples.
def mapper(a):
return (a, 1)
r = list(map(lambda a: mapper(a), arr));
//output example:
//(11817685, 1), (2014036792, 1), (2014047115, 1), (11817685, 1)
我期望reduce函数可以帮助我按每个元组中的第一个数字(id)对计数进行分组.例如:
I'm expecting the reduce function can help me to group counts by the first number (id) in each tuple. For example:
(11817685, 2), (2014036792, 1), (2014047115, 1)
我尝试了
cnt = reduce(lambda a, b: a + b, r);
和其他一些方法,但是它们都不能解决问题.
and some other ways but they all don't do the trick.
注意 感谢您提供其他解决问题的方法的建议,但是我只是在这里学习Python以及如何实现map-reduce,并且我已经将我的实际业务问题简化了很多,以使其易于理解,因此,请您多多包涵.告诉我做地图减少的正确方法.
NOTE Thanks for all the advice on other ways to solve the problems, but I'm just learning Python and how to implement a map-reduce here, and I have simplified my real business problem a lot to make it easy to understand, so please kindly show me a correct way of doing map-reduce.
推荐答案
您可以使用Counter
:
from collections import Counter
arr = [11817685, 2014036792, 2014047115, 11817685]
counter = Counter(arr)
print zip(counter.keys(), counter.values())
由@ShadowRanger指出Counter
具有items()
方法:
As pointed by @ShadowRanger Counter
has items()
method:
from collections import Counter
arr = [11817685, 2014036792, 2014047115, 11817685]
print Counter(arr).items()
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