Python字典 - 从其他值查找平均值 [英] Python Dictionary - find average of value from other values

问题描述

我有以下列表

  count = 3.5，price = 2500 
 
 count = 3 ，price = 400 
 
 count = 2，price = 3000 
 
 count = 3.5，price = 750 
 
 count = 2，price = 500 
  

我想查找所有计数相同的平均价格。例如：

  count = 2，price = 3000 
 
 count = 2，price = 500 
 
 3000 + 500 = 3500 
 
 3500/2 = 1750 
  

2的平均值是1750

这是我的代码到目前为止

  avg_list = [value [average] for dictionary in dictionary_database_list] 
 
 counter_obj = collections.Counter（count_list）
 
 print（AVG：）
 
在我的counter_obj中：
 
 print（i，counter_obj [i]）
  / pre> 
 
解决方案
我承认我不是100％清楚你在找什么，我会给它一个镜头：
 
 
 
当你想迭代一个事物列表并积累某些关于同一事物的信息时，一个很好的策略是使用哈希表。在Python中，我们通常对需要哈希表的算法使用 dict 。
 
 
 
收集足够的信息以获取您的列表中每个项目的平均价格，我们需要：
 
 
 a）具有特定count的项目总数< b> b）具有特定计数的项目的总价格
 
 
所以让我们建立一个数据结构，将一个count映射到含有count的项目的total items和total price的单词。
 
 
 
我们的输入格式为：
  item_list = [
 {'count'：3.5，'price'：2500} ，
 {'count'：3，'price'：400}，
 {'count'：2，'price'：3000}，
 {'count'：3.5，'price '：750}，
 {'count'：2，'price'：500}，
] 
  
现在我们来映射关于总项目和总价格的信息在一个 dict 中 items_by_count ：
  item_list中的项目：
计数， price = item ['count']，item ['price'] 
 items_by_count [count] ['total_items'] + = 1 
 items_by_count [count] ['total_price'] + = price 
  
 但等待！  items_by_count [count] 将抛出 KeyError ，如果 count 不在dict中。这是  defaultdict  。让我们将我们从未见过的 count 的默认值定义为0总价，以及0个总项：
  from collections import defaultdict 
 items_by_count = defaultdict（lambda：{
'total_items'：0，
'total_price'：0 
} ）
  
 现在我们的代码每次看到都不会抛出异常计数的新值。
 
 
 
最后，我们需要实际取平均值。让我们在另一个 dict 中获取我们需要的信息，映射到平均价格。对于词汇理解，这是一个很好的用例：
  {count：item ['total_price'] / item ['total_items'] 
为count，item_by_count.iteritems（）中的项
  
这将遍历 items_by_count  dict，并创建我们想要的新dict。 > 
 
 
将它们放在一起：
 从集合import defaultdict 
 
 def get_average_price（item_list）：
 items_by_count = defaultdict（lambda：{
'total_items'：0，
'total_price'：0 
}）
 
 item_list中的项目：
 count，price = item ['count']，item ['price'] 
 items_by_count [count] ['total_items'] + = 1 
 items_by_count [count] ['total_price'] + = price 
 
 return {count：item ['total_price'] / item ['total_items'] 
用于计数，项目中的项目_by_count.iteritems（）} 
  
如果我们传入我们的例子输入dict，这个函数返回：
  {3.5：1625，2：1750，3：400}  
 
 
 
希望你想要的输出！谨慎的浮动部分在您的特定Python版本。
 
I have the following list
count = 3.5, price = 2500

count = 3, price = 400

count = 2, price = 3000

count = 3.5, price = 750

count = 2, price = 500
I want to find the average price for all where the count is the same.  For example:
count = 2, price = 3000

count = 2, price = 500

3000 + 500 = 3500

3500/2 = 1750
Avg for 'count 2' is 1750

Here's my code so far
avg_list = [value["average"] for value in dictionary_database_list] 

counter_obj = collections.Counter(count_list)

print ("AVG:")

for i in counter_obj:

    print (i, counter_obj[i])

解决方案
I'll admit I'm not 100% clear on what you're looking for here, but I'll give it a shot:

A good strategy when you want to iterate over a list of "things" and accumulate some kind of information about "the same kind of thing" is to use a hash table. In Python, we usually use a dict for algorithms that require a hash table.

To collect enough information to get the average price for each item in your list, we need:

  
a) the total number of items with a specific "count"
  
  
b) the total price of items with a specific "count"
So let's build a data structure that maps a "count" to a dict containing "total items" and "total price" for the item with that "count".

Let's take our input in the format:
item_list = [
    {'count': 3.5, 'price': 2500},
    {'count': 3, 'price': 400},
    {'count': 2, 'price': 3000},
    {'count': 3.5, 'price': 750},
    {'count': 2, 'price': 500},
]
Now let's map the info about "total items" and "total price" in a dict called items_by_count:
for item in item_list:
    count, price = item['count'], item['price']
    items_by_count[count]['total_items'] += 1
    items_by_count[count]['total_price'] += price
But wait! items_by_count[count] will throw a KeyError if count isn't already in the dict. This is a good use case for defaultdict. Let's define the default value of a count we've never seen before as 0 total price, and 0 total items:
from collections import defaultdict
items_by_count = defaultdict(lambda: {
    'total_items': 0,
    'total_price': 0
})
Now our code won't throw an exception every time we see a new value for count.

Finally, we need to actually take the average. Let's get the information we need in another dict, mapping count to average price. This is a good use case for a dict comprehension:
{count: item['total_price'] / item['total_items']
for count, item in items_by_count.iteritems()}
This iterates over the items_by_count dict and creates the new dict that we want.

Putting it all together:
from collections import defaultdict

def get_average_price(item_list):
    items_by_count = defaultdict(lambda: {
        'total_items': 0,
        'total_price': 0
    })

    for item in item_list:
        count, price = item['count'], item['price']
        items_by_count[count]['total_items'] += 1
        items_by_count[count]['total_price'] += price

    return {count: item['total_price'] / item['total_items']
            for count, item in items_by_count.iteritems()}
If we pass in our example input dict, this function returns:
{3.5: 1625, 2: 1750, 3: 400}

Which is hopefully the output you want! Be cautious of gotchas like float division in your particular Python version.

                        
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