使用python，通過從列表中提取key:value來創建字典

Question

我需要從 list1 制作兩個字典：

list1 = [['8/16/2016 9:55', 6], ['11/22/2015 13:43', 29], ['5/2/2016 10:14', 1],
['8/2/2016 14:20', 3], ['10/15/2015 16:38', 17], ['9/26/2015 23:23', 1],
['4/22/2016 12:24', 4], ['11/16/2015 9:22', 1], ['2/24/2016 17:57', 1], 
['6/4/2016 17:17', 2]]

count_by_hour = {} # this is created by extracting the hour from index[0] of list1

在對我之前發布的問題的回復的幫助下，我能夠得到這個。

for each in list1:
   if each[0].split(':')[0][-2] == " ": #split by : to get second last char and check if >9
   hours.append(each[0].split(':')[0][-1:]) # if hour is <9 take last char which is hour
else:
   hours.append(each[0].split(':')[0][-2:]) #else take last 2 chars
print('Hour extracted:')
print(hours)

輸出：

Counts by hour:
{'9': 2, '13': 1, '10': 1, '14': 1, '16': 1, '23': 1, '12': 1, '17': 2}

現在，我該如何執行以下操作：

comments_by_hour = {}

Expected Outcome:
{9:7, 13:29, 10:1, 14:3, 16:17, 23:1, 12:4, 17:2} #value is a total for every hour that exists as a key in list1

與往常一樣，任何幫助表示贊賞。

Answer 1

請注意，我們需要為許多類別（小時）中的每一個單獨累加總和。 一個簡單的解決方案（在純 Python 中）結合了累加器模式，同時使用字典來存儲所有計數。

首先，讓我們使用time.strptime使用列表time.strptime來提取小時數。

In [1]: list1 = [['8/16/2016 9:55', 6], ['11/22/2015 13:43', 29], ['5/2/2016 10:14', 1],
      : ['8/2/2016 14:20', 3], ['10/15/2015 16:38', 17], ['9/26/2015 23:23', 1],
      : ['4/22/2016 12:24', 4], ['11/16/2015 9:22', 1], ['2/24/2016 17:57', 1],
      : ['6/4/2016 17:17', 2]]

In [2]:  from time import strptime

In [3]: hour_list = [(strptime(time, "%m/%d/%Y %H:%M").tm_hour, val) for time, val in list1]

解決方案是使用字典來累積每個類別的統計信息。 通過（a）從一個空字典開始並（b）更新每個新值的總和來做到這一點。 這可以如下完成。

In [4]: comments_by_hour = {}

In [5]: for hour, val in hour_list:
      :     comments_by_hour[hour] = val + comments_by_hour.get(hour, 0)
      :

In [6]: comments_by_hour
Out[6]: {9: 7, 13: 29, 10: 1, 14: 3, 16: 17, 23: 1, 12: 4, 17: 3}

請注意， comments_by_hour.get(hour, 0)用於獲取該小時的當前值（如果存在），否則使用默認值 0。