R中匹配的python(或numpy)等效项

问题描述

在python中，有什么简单的方法可以完成R函数中的match函数?R中的match所执行的操作是返回其第一个参数在其第二个参数中(第一个)匹配位置的向量.

Is there any easy way in python to accomplish what the match function does in R?what match in R does is that it returns a vector of the positions of (first) matches of its first argument in its second.

例如，以下R代码段.

For example, the following R snippet.

> a <- c(5,4,3,2,1)
> b <- c(2,3)
> match(a,b)
[1] NA NA  2  1 NA

在python中进行翻译，我正在寻找的是执行以下操作的函数

Translate that in python, what I am looking for is a function that does the following

>>> a = [5,4,3,2,1]
>>> b = [2,3]
>>> match(a,b)
[None, None, 2, 1, None]

谢谢！

推荐答案

>>> a = [5,4,3,2,1]
>>> b = [2,3]
>>> [ b.index(x) if x in b else None for x in a ]
[None, None, 1, 0, None]

如果您确实需要位置基于一个"而不是零基于"，则加1.

Add 1 if you really need position "one based" instead of "zero based".

>>> [ b.index(x)+1 if x in b else None for x in a ]
[None, None, 2, 1, None]

如果要重复很多，可以使这种单线可重用:

You can make this one-liner reusable if you are going to repeat it a lot:

>>> match = lambda a, b: [ b.index(x)+1 if x in b else None for x in a ]
>>> match
<function <lambda> at 0x04E77B70>
>>> match(a, b)
[None, None, 2, 1, None]

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