笨拙的字典顺序 [英] Numpy lexicographic ordering

问题描述

我想按字典顺序对以下数组 a 进行排序(获取索引位置)，但是，我在理解numpy结果时遇到了问题:

I'd like to lexicographically sort the following array a (get index positions), but, I'm having problems understanding the numpy results:

>>> a = np.asarray([[1, 1, 1, 2, 1, 2], [2, 1, 2, 3, 1, 0], [1, 2, 3, 3, 2, 2]])
>>> a
array([[1, 1, 1, 2, 1, 2],
       [2, 1, 2, 3, 1, 0],
       [1, 2, 3, 3, 2, 2]])
>>> np.lexsort(a)
array([0, 5, 1, 4, 2, 3])

例如，我不明白为什么[1, 2, 1](a[:,0])是排序索引0而[1, 1, 2](a[:,1])是索引5，甚至认为它应该比[1, 2, 1]还要小. /p>

For instance, I don't understand why [1, 2, 1] (a[:,0]) is sort-index 0 while [1, 1, 2] (a[:,1]) is index 5, even thought it should be samller than [1, 2, 1].

推荐答案

键的重要性顺序与您期望的相反. 为了获得预期的结果，只需将矩阵上下颠倒

The order of significance for keys is opposite to what you expected. In order to get expected result just flip the matrix upside down

>>> np.lexsort(np.flipud(a))
array([1, 4, 0, 2, 5, 3])

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