获取列表中每个元素首次出现的索引? [英] Get indexes for first occurrence of each element in a list?

问题描述

我有一个大约90k元素的列表(大约670个唯一元素).我想获取每个值的第一次出现的索引.我刚刚尝试过这样的列表理解:

I have a list of about 90k elements (about 670 unique). I would like to get the indexes for the first occurrence of each value. I have just tried a list comprehension like this:

In: [["foo", "bar", "baz", "bar", "foo"].index(x) for x in ["foo", "bar", "baz", "bar", "foo"]]
Out: [0, 1, 2, 1, 0]

这可行，但是要花几分钟才能在我的机器上运行.什么是更好(更快)的方法?

This works, but it takes a couple of minutes to run on my machine. What is a better (faster) way to do this?

推荐答案

我认为您只想使用 enumerate (除非您想要列表中每个项目的第一个出现):

I think you just want to use enumerate (unless you want the first occurrence of each item in the list):

strings = ["foo", "bar", "baz", "bar", "foo"]
for index, value in enumerate(strings):
    print index, value

输出

0 foo
1 bar
2 baz
3 bar
4 foo

例如，如果要使用 1 bar 而不是 3 bar ，则可以维护找到的字符串的字典:

If you wanted, for example, 1 bar instead of 3 bar, you can maintain a dictionary of found strings:

for index, value in enumerate(strings):
    if value not in d:
        d[value] = index

for value in strings:
    print value, d[value]

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