Numpy：按键功能排序 [英] Numpy: sort by key function

问题描述

有没有办法使用键（或比较器）函数对numpy ndarray的行进行排序，而无需转换为python列表？

特别是，我需要根据这个函数进行排序：

  c1，c2 = 4,7 
 lambda row：c1 *（row [1] / c2）+ row [0] 
  

我意识到一个可能的解决方案是用每行的关键值生成一个向量，但是如何根据它来排序呢？是否应该试图将这种向量转换为索引向量？

  order = c1 *（matrix [：，1] / c2 ）+ matrix [：，0] 
 indexes = order_to_index（order）
 return matrix [indexes] 
  

这是否现实？

解决方案

您的方法是正确的，它类似于 Schwartzian transform 或 Decorate-Sort-Undecorate（DSU）idiom 正如我所说的，你可以使用numpy函数 np.argsort 。它完成了 order_to_index 的工作。

Is there a way to sort the rows of a numpy ndarray using a key (or comparator) function, without resorting to converting to a python list?

In particular, I need to sort according to this function:

c1,c2= 4,7
lambda row: c1*(row[1]/c2)+row[0]

I realise one possible solution would be to generate a vector with the key value of each row, but how would one sort according to it? Should one seek to convert such vector into a index vector somehow?

order= c1*(matrix[:,1]/c2)+matrix[:,0]
indexes= order_to_index( order )
return matrix[ indexes ]

Is this realistic?

解决方案

your approach is right, it is similar to the Schwartzian transform or Decorate-Sort-Undecorate (DSU) idiom

As I said you can use the numpy function np.argsort. It does the work of your order_to_index.

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