numpy.unique，保留顺序 [英] numpy.unique with order preserved

问题描述

['b','b','b','a','a','c','c']

numpy.unique提供

numpy.unique gives

['a','b','c']

如何保存原始订单

['b','a','c']

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好答案.奖金问题.为什么这些方法都不适用于该数据集? http://www.uploadmb.com/dw.php?id=1364341573 这是 numpy排序奇怪行为的问题

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Great answers. Bonus question. Why do none of these methods work with this dataset? http://www.uploadmb.com/dw.php?id=1364341573 Here's the question numpy sort wierd behavior

推荐答案

unique()很慢，O(Nlog(N))，但是您可以通过以下代码来做到这一点:

unique() is slow, O(Nlog(N)), but you can do this by following code:

import numpy as np
a = np.array(['b','a','b','b','d','a','a','c','c'])
_, idx = np.unique(a, return_index=True)
print(a[np.sort(idx)])

输出:

['b' 'a' 'd' 'c']

对于大数组O(N)，

Pandas.unique()要快得多:

Pandas.unique() is much faster for big array O(N):

import pandas as pd

a = np.random.randint(0, 1000, 10000)
%timeit np.unique(a)
%timeit pd.unique(a)

1000 loops, best of 3: 644 us per loop
10000 loops, best of 3: 144 us per loop

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