Question

我正在尝试从列表和元组元组创建字典，如下所示。我必须将元组反向映射到列表并创建一组非None列名。

非常感谢任何关于pythonic方式实现解决方案的建议（所需词典）。

MySQL表'StateLog'：

Name NY   TX   NJ
Amy  1    None 1
Kat  None 1    1
Leo  None None 1

Python代码：

## Fetching data from MySQL table
#cursor.execute("select * from statelog")
#mydataset = cursor.fetchall()
## Fetching column names for mapping
#state_cols = [fieldname[0] for fieldname in cursor.description]

state_cols = ['Name', 'NY', 'TX', 'NJ']
mydataset = (('Amy', '1', None, '1'), ('Kat', None, '1', '1'), ('Leo', None, None, '1'))

temp = [zip(state_cols, each) for each in mydataset]

# Looks like I can't do a tuple comprehension for the following snippet : finallist = ((eachone[1], eachone[0]) for each in temp for eachone in each if eachone[1] if eachone[0] == 'Name')
for each in temp:
    for eachone in each:
        if eachone[1]:
            if eachone[0] == 'Name':
                k = eachone[1]
            print k, eachone[0]

print '''How do I get a dictionary in this format'''            
print '''name_state = {"Amy": set(["NY", "NJ"]),
                "Kat": set(["TX", "NJ"]),
                "Leo": set(["NJ"])}'''

到目前为止的输出：

Amy Name
Amy NY
Amy NJ
Kat Name
Kat TX
Kat NJ
Leo Name
Leo NJ

所需词典：

name_state = {"Amy": set(["NY", "NJ"]),
              "Kat": set(["TX", "NJ"]),
              "Leo": set(["NJ"])}

Answer 1

看起来像defaultdict的另一份工作！

所以我们创建我们的默认字典

name_state = collections.defaultdict(set)

我们现在有一个字典设置为所有默认值，我们现在可以做这样的事情

name_state['Amy'].add('NY')

继续前进你只需要迭代你的对象并为每个名称添加正确的状态。享受

Answer 2

您可以将其作为字典理解（Python 2.7 +）：

from itertools import compress
name_state = {data[0]: set(compress(state_cols[1:], data[1:])) for data in mydataset}

或作为生成器表达式：

name_state = dict((data[0], set(compress(state_cols[1:], data[1:]))) for data in mydataset)

Answer 3

说实话，我会说你的问题是你的代码变得太麻烦了。抵制“一线”的诱惑，创造一种功能。一切都会变得更容易！

mydataset = (
        ('Amy', '1', None, '1'),
        ('Kat', None, '1', '1'),
        ('Leo', None, None, '1')
)

def states(cols, data):
    """
    This function receives one of the tuples with data and returns a pair
    where the first element is the name from the tuple, and the second
    element is a set with all matched states. Well, at least *I* think
    it is more readable :)
    """
    name = data[0]
    states = set(state for state, value in zip(cols, data) if value == '1')
    return name, states

pairs = (states(state_cols, data) for data in mydataset)
# Since dicts can receive an iterator which yields pairs where the first one
# will become a key and the second one will become the value, I just pass
# a list with all pairs to the dict constructor.
print dict(pairs)

结果是：

{'Amy': set(['NY', 'NJ']), 'Leo': set(['NJ']), 'Kat': set(['NJ', 'TX'])}

如何在给定列表和元组元组的情况下创建将字符串映射到集合的字典？

3 个答案: