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Python implements a method to extract subsets from a dictionary (code)

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Release： 2018-10-23 16:11:49

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The content of this article is about the method (code) of extracting subsets from the dictionary in Python. It has certain reference value. Friends in need can refer to it. I hope it will be helpful to you.

1. Requirements

We want to create a dictionary, which itself is a subset of another dictionary.

2. Solution

It can be easily solved using dictionary derivation.

prices={
'a':1.1,
'b':2.2,
'c':3.3,
'd':4.4,
'e':5.5
}
p1={key:value for key ,value in prices.items() if value>3}
print(p1)

names={'a','b'}
p2={key:value for key,value in prices.items() if key in names}
print(p2)

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Result:

{'c': 3.3, 'd': 4.4, 'e': 5.5}
{'a': 1.1, 'b': 2.2}

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3. Analysis

Most of the problems that can be solved by dictionary derivation can also be solved by creating a sequence of tuples and then They are passed to the dict() function to complete, for example:

#结果为：{'c': 3.3, 'd': 4.4, 'e': 5.5}
p3=dict((key,value) for key,value in prices.items() if value>3)

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But the dictionary derivation method is clearer and actually runs much faster. (The first efficiency will be nearly 2 times faster)

Sometimes there are multiple ways to complete the same thing in the same time. For example, the second example can also be rewritten as:

#结果为：{'b': 2.2, 'a': 1.1}
p4={key:prices[key] for key in prices.keys() & names}

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However, tests show that this solution is almost 1.6 times slower than the first one. Therefore, when there are multiple solutions to the same problem, you can do a little test to study the time spent.

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