Python - 从 CSV 创建字典字典

Question

我有一个 CSV，其中第一列有许多重复值，第二列是映射到第三列中的值的预定代码，例如：

1, a, 24
1, b, 13
1, c, 30
1, d, 0
2, a, 1
2, b, 12
2, c, 82
2, d, 81
3, a, 04
3, b, 23
3, c, 74
3, d, 50

我正在尝试从 CSV 创建字典字典，结果如下：

dict 1 = {'1':{'a':'24', 'b':'13', 'c':'30','d':'0'}, 
          '2':{'a':'1', 'b':'12', 'c':'82','d':'81'}, 
          ... }

我的代码可以很好地创建键值，但是结果值字典都是空的（尽管一些打印语句显示它们不在运行过程中）...

with open(file, mode='rb') as csvfile:
    reader = csv.reader(csvfile, delimiter=',')

    dict1 = {}  # creates main dict
    for row in reader:  # iterates through the rows of the csvfile
        if row[0] in dict1:
            dict2[row[1]] = row[2]  # adds another key, value to dict2
        else:
            dict1[row[0]] = {}  # creates a new key entry for the new      dict1 key
            dict2 = {}  # creates a new dict2 to start building as the value for the new dict1 key
            dict2[row[1]] = row[2]  # adds the first key, value pair for dict2

Answer 1

为此使用collections.defaultdict。

import collections

with open(file, mode='rb') as csvfile:
    reader = csv.reader(csvfile, delimiter=',')

    dict1 = collections.defaultdict(dict)
    for row in reader:
        dict1[row[0]][row[1]] = row[2]

defaultdict 只不过是一个字典，它使用默认值初始化未知键的值。这里，默认是初始化第二个新字典（dict 是字典构造函数）。因此，您可以轻松地将两个映射设置在同一行中。

Answer 2

您不需要dict2，并且您也没有将其设置为值字典。试试这个修改后的版本：

with open(file, mode='rb') as csvfile:
    reader = csv.reader(csvfile, delimiter=',')

    dict1 = {}  # creates main dict
    for row in reader:  # iterates through the rows of the csvfile
        if row[0] not in dict1:
            dict1[row[0]] = {}  # creates a new key entry for the new dict1 key
        dict1[row[0]][row[1]] = row[2]  # adds another key, value to dict2

您也可以使用defaultdict 跳过检查现有密钥。