如何按多维数组的第一列搜索唯一元素 [英] how to search for unique elements by the first column of a multidimensional array

问题描述

我试图找到一种方法，如何通过仅获取第一列中唯一的元素来从多维数组创建新数组，例如，如果我有一个数组

I am trying to find a way how to create a new array from a multidimensional array by taking only elements that are unique in the first column, for example if I have an array

[[1,2,3],
[1,2,3],
[5,2,3]]

操作后我想得到这个输出

After the operation I would like to get this output

[[1,2,3],
[5,2,3]]

显然第二列和第三列不需要是唯一的.

Obviously the second an third columns do not need to be unique.

谢谢

推荐答案

由于您希望保留第一行的第一列唯一性，您只需使用 np.unique 及其可选的 return_index 参数，它将为您提供 A[:,0] 元素的唯一性中第一个出现的索引(从而满足第一行标准)，其中A 是输入数组.因此，我们将有一个矢量化的解决方案，就像这样 -

Since you are looking to keep the first row of first column uniqueness, you can just use np.unique with its optional return_index argument which will give you the first occurring index (thus fulfils the first row criteria) among the uniqueness on A[:,0] elements, where A is the input array. Thus, we would have a vectorized solution, like so -

_,idx = np.unique(A[:,0],return_index=True)
out = A[idx]

样品运行 -

In [16]: A
Out[16]: 
array([[1, 2, 3],
       [5, 2, 3],
       [1, 4, 3]])

In [17]: _,idx = np.unique(A[:,0],return_index=True)
    ...: out = A[idx]
    ...: 

In [18]: out
Out[18]: 
array([[1, 2, 3],
       [5, 2, 3]])

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