如何从字典列表中提取特定键的所有值？ [英] How do I extract all the values of a specific key from a list of dictionaries?

问题描述

我有一个列表，列表中都有相同的结构。例如：

I have a list of dictionaries that all have the same structure within the list. For example:

test_data = [{'id':1, 'value':'one'}, {'id':2, 'value':'two'}, {'id':3, 'value':'three'}]

我想从列表中的每个字典中获取每个值项目：

I want to get each of the value items from each dictionary in the list:

['one', 'two', 'three']

我可以遍历列表并使用for循环来提取每个值：

I can of course iterate through the list and extract each value using a for loop:

results = []
for item in test_data:
    results.append(item['value'])

但是我的数据集相当大。我想知道是否有更快的方法。

however my data set is quite large. I'm wondering if there's a faster way to this.

推荐答案

如果您只需要迭代一次值，请使用生成器表达式：

If you just need to iterate over the values once, use the generator expression:

generator = ( item['value'] for item in test_data )

...

for i in generator:
    do_something(i)

<另一个（深奥）选项可能是使用 map 与 itemgetter - 它可能比生成器表达式稍快，否则，取决于具体情况：

Another (esoteric) option might be to use map with itemgetter - it could be slightly faster than the generator expression, or not, depending on circumstances:

from operator import itemgetter

generator = map(itemgetter('value'), test_data)

如果你绝对需要一个列表，列表的理解速度比迭代 list.append ，因此：

And if you absolutely need a list, a list comprehension is faster than iterated list.append, thus:

results = [ item['value'] for item in test_data ]

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