使用具有布尔表达式的数组从列表中提取值 [英] Extract values from a list using an array with boolean expressions

问题描述

我有一个这样的元组列表:

I have a list of tuples like this:

listOfTuples = [(0, 1), (0, 2), (3, 1)]

和一个看起来像这样的数组:

and an array that could look like this:

myArray = np.array([-2, 9, 5])

此外，我有一个数组，该数组包含我创建的布尔表达式，如下所示:

Furthermore, I have an array with Boolean expressions which I created like this:

dummyArray = np.array([0, 1, 0.6])
myBooleanArray =  dummyArray < 1

myBooleanArray因此看起来像这样:

array([True, False, True], dtype=bool)

现在，我想基于myBooleanArray从listOfTuples和myArray中提取值.对于myArray，它很简单，我可以使用:

Now I would like to extract values from listOfTuples and myArray based on myBooleanArray. For myArray it is straight forward and I can just use:

myArray[myBooleanArray]

这给了我想要的输出

[-2  5]

但是，当我使用

listOfTuples[myBooleanArray]

我收到

TypeError:只有具有一个元素的整数数组可以转换为 索引

TypeError: only integer arrays with one element can be converted to an index

一种解决方法是先通过执行以下操作将此列表转换为数组:

A workaround would be to convert this list to an array first by doing:

np.array(listOfTuples)[myBooleanArray]

产生

[[0 1]
 [3 1]]

有没有更聪明的方法?我想要的输出将是

Is there any smarter way of doing this? My desired output would be

[(0, 1), (3, 1)]

推荐答案

您已经做了最好的方法，但是如果您正在寻找python解决方案，则可以使用itertools.compress

Already you have done the best way,but if you are looking for a python solution you can use itertools.compress

>>> from itertools import compress
>>> list(compress(listOfTuples,bool_array))
[(0, 1), (3, 1)]

compress的优点之一是，如果列表很大，它会返回生成器，并且效率很高.因为使用生成器可以节省很多内存.

One of the advantage of compress is that it returns a generator and its very efficient if you have huge list. because you'll save much memory with using generators.

如果您要遍历结果，则无需转换为列表.您可以这样做:

And if you want to loop over the result you don't need convert to list. You can just do :

for item in compress(listOfTuples,bool_array):
     #do stuff

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