如何将dict.get()与多维dict一起使用? [英] How to use dict.get() with multidimensional dict?

问题描述

我有一个多维字典，我希望能够通过key:key对来检索值，如果第一个键不存在，则返回'NA'.所有子小格都具有相同的键.

I have a multidimensional dict, and I'd like to be able to retrieve a value by a key:key pair, and return 'NA' if the first key doesn't exist. All of the sub-dicts have the same keys.

d = {   'a': {'j':1,'k':2},
        'b': {'j':2,'k':3},
        'd': {'j':1,'k':3}
    }

我知道我可以使用 d.get('c'，'NA')来获取子字典(如果存在)，否则返回'NA'，但是我真的只需要一个值从子命令.我想做类似 d.get('c ['j']'，'NA')的事情.

I know I can use d.get('c','NA') to get the sub-dict if it exists and return 'NA' otherwise, but I really only need one value from the sub-dict. I'd like to do something like d.get('c['j']','NA') if that existed.

现在，我只是检查顶级键是否存在，然后将子值(如果存在)分配给变量，如果不存在，则将其分配给'NA'.但是，我这样做大约有50万次，并且还从其他地方检索/生成有关每个顶级密钥的其他信息，我正在尝试加快这一速度.

Right now I'm just checking to see if the top-level key exists and then assigning the sub-value to a variable if it exists or 'NA' if not. However, I'm doing this about 500k times and also retrieving/generating other information about each top-level key from elsewhere, and I'm trying to speed this up a little bit.

推荐答案

如何

d.get('a', {'j': 'NA'})['j']

?

如果不是所有下属都具有 j 键，则

If not all subdicts have a j key, then

d.get('a', {}).get('j', 'NA')

 

要减少创建的相同对象，可以设计类似

To cut down on identical objects created, you can devise something like

class DefaultNASubdict(dict):
    class NADict(object):
        def __getitem__(self, k):
            return 'NA'

    NA = NADict()

    def __missing__(self, k):
        return self.NA

nadict = DefaultNASubdict({
                'a': {'j':1,'k':2},
                'b': {'j':2,'k':3},
                'd': {'j':1,'k':3}
            })

print nadict['a']['j']  # 1
print nadict['b']['j']  # 2
print nadict['c']['j']  # NA

 

使用 defaultdict 的相同想法:

import collections

class NADict(object):
    def __getitem__(self, k):
        return 'NA'

    @staticmethod
    def instance():
        return NADict._instance

NADict._instance = NADict()


nadict = collections.defaultdict(NADict.instance, {
                'a': {'j':1,'k':2},
                'b': {'j':2,'k':3},
                'd': {'j':1,'k':3}
            })

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