按列对NumPy浮点数组进行排序 [英] Sort NumPy float array column by column

问题描述

遵循此技巧，它可以获取NumPy数组的唯一条目，现在有一个两列数组，基本上是成对的，第一个元素的范围为[0.9:0.02:1.1]，第二个元素的范围为[1.5:0.1:2.0].我们将此称为A.目前，它是完全未分类的，即

Following this trick to grab unique entries for a NumPy array, I now have a two-column array, basically of pairs with first element in the range [0.9:0.02:1.1] and the second element in the range [1.5:0.1:2.0]. Let's call this A. Currently, it's completely unsorted, i.e.

In [111]: A
Out[111]: 
array([[ 1.1 ,  1.9 ],
       [ 1.06,  1.9 ],
       [ 1.08,  1.9 ],
       [ 1.08,  1.6 ],
       [ 0.9 ,  1.8 ],
       ...
       [ 1.04,  1.6 ],
       [ 0.96,  2.  ],
       [ 0.94,  2.  ],
       [ 0.98,  1.9 ]])

我想对它进行排序，以使每一行都在第二列中增加，然后在第一列中增加.即

I'd like to sort it so that each row first increases in the second column, then the first. i.e.

array([[ 0.9 ,  1.5 ],
       [ 0.9 ,  1.6 ],
       [ 0.9 ,  1.7 ],
       [ 0.9 ,  1.9 ],
       [ 0.9 ,  1.9 ],
       [ 0.9 ,  2.  ],
       [ 0.92,  1.5 ],
       ...
       [ 1.08,  2.  ],
       [ 1.1 ,  1.5 ],
       [ 1.1 ,  1.6 ],
       [ 1.1 ,  1.7 ],
       [ 1.1 ,  1.8 ],
       [ 1.1 ,  1.9 ],
       [ 1.1 ,  2.  ]])

但是我找不到同时提供两者的排序算法.根据建议的此处，我尝试了A[A[:,0].argsort()]和A[A[:,1].argsort()]，但它们仅对一列进行排序.我也尝试过同时使用这两种方法，但同样的事情也会发生.

but I can't find a sort algorithm that gives both. As suggested here, I've tried A[A[:,0].argsort()] and A[A[:,1].argsort()], but they only sort one column each. I've also tried applying both but the same thing happens.

如果我错过了一些简单的事情，我深表歉意，但是我已经找了一段时间了...

I apologize if I've missed something simple but I've been looking for this for a while now...

推荐答案

numpy.lexsort 将在这里工作:

numpy.lexsort will work here:

A[np.lexsort(A.T)]

在将A传递给lexsort之前，需要进行转置，因为在传递2d数组时，它希望按行(最后一行，倒数第二行等)进行排序.

You need to transpose A before passing it to lexsort because when passed a 2d array it expects to sort by rows (last row, second last row, etc).

另一种可能稍微清晰的方法是显式传递列:

The alternative possibly slightly clearer way is to pass the columns explicitly:

A[np.lexsort((A[:, 0], A[:, 1]))]

您仍然需要记住lexsort首先按最后一个键排序(这可能有一定的道理；这与对连续键执行稳定排序相同).

You still need to remember that lexsort sorts by the last key first (there's probably some good reason for this; it's the same as performing a stable sort on successive keys).

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