尝试通过计算列表列表中的出现次数来添加字典值(Python)

问题描述

I'm trying to get a count of items in a list of lists and add those counts to a dictionary in Python. I have successfully made the list (it's a list of all possible combos of occurrences for individual ad viewing records) and a dictionary with keys equal to all the values that could possibly appear, and now I need to count how many times each occur and change the values in the dictionary to the count of their corresponding keys in the list of lists. Here's what I have:

import itertools
stuff=(1,2,3,4)
n=1
combs=list()
while n<=len(stuff):
    combs.append(list(itertools.combinations(stuff,n)))
    n = n+1
viewers=((1,3,4),(1,2,4),(1,4),(1,2),(1,4)) 
recs=list()
h=1
while h<=len(viewers):
    j=1
    while j<=len(viewers[h-1]):
       recs.append(list(itertools.combinations(viewers[h-1],j))) 
       j=j+1
    h=h+1
showcount={}
for list in combs:
    for item in list:
        showcount[item]=0    
for k, v in showcount:
        for item in recs:
            for item in item:
                if item == k:
                    v = v+1

I've tried a bunch of different ways to do this, and I usually either get 'too many values to unpack' errors or it simply doesn't populate. There are several similar questions posted but I'm pretty new to Python and none of them really addressed what I needed close enough for me to figure it out. Many thanks.

解决方案

Use a Counter instead of an ordinary dict to count things:

from collections import Counter

showcount = Counter()
for item in recs:
    showcount.update(item)

or even:

from collections import Counter
from itertools import chain

showcount = Counter(chain.from_iterable(recs))

As you can see that makes your code vastly simpler.