从字典列表中返回在特定键中具有最高值的字典 [英] Return the dictionary from a list of dictionaries with the highest value in a specific key

问题描述

我在python中有以下字典列表:

I have the following list of dictionaries in python:

data = [{'flag': 'one', 'timestamp': 20190710},
{'flag': 'one', 'timestamp': 20190711},
{'flag': 'two', 'timestamp': 20190712}, 
{'flag': 'two', 'timestamp': 20190709}]

我想返回在键 timestamp 中具有最高值并且在键 flag 中具有值 one 的字典.

I would like to return the dictionary with the the highest value in the key timestamp and with the value one in the key flag.

我在这里做了类似的事情:

I have done something similar here:

根据Python中的条件返回字典中最大值的键

但是不能使其在此新设置中起作用.

But cannot make it work in this new set-up.

推荐答案

您可以将 max()内置函数与自定义 key = 一起使用.在此之前，我们仅对键为'flag' == 'one':

You could use max() built-in function with custom key=. Before that, we filter the dictionary only for items with key 'flag' == 'one':

data = [{'flag': 'one', 'timestamp': 20190710},
{'flag': 'one', 'timestamp': 20190711},
{'flag': 'two', 'timestamp': 20190712},
{'flag': 'two', 'timestamp': 20190709}]

print(max((i for i in data if i['flag'] == 'one'), key=lambda k: k['timestamp']))

打印:

{'flag': 'one', 'timestamp': 20190711}

什么更快的快速基准测试-首先进行过滤或在整个列表中找到最大值:

Quick benchmark of what's faster - doing the filtration first or finding the max in whole list:

from random import choice,randint

data = []
for i in range(10000):
    data.append({'flag': choice(['one', 'two']), 'timestamp': randint(1, 1_000_000)})

def fn1():
    return max(data, key=lambda x: (x["flag"] == 'one', x["timestamp"]))

def fn2():
    return max((i for i in data if i['flag'] == 'one'), key=lambda k: k['timestamp'])

from timeit import timeit

t1 = timeit(lambda: fn1(), number=1_000)
t2 = timeit(lambda: fn2(), number=1_000)

print(t1)
print(t2)

打印:

1.5405012619994523
0.8562619980002637

这意味着首先进行过滤会更快.

Which means doing the filtration first is faster.

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