问题

我见过这个语句：

x[:, 0:4]

我对此有些困惑。有人能解释一下它在列表索引方面的含义吗？

英文:

I have seen this statement:

x[:, 0:4]

I'm a little confused by this. Can anyone explain what it means in terms of indexes into a list?

答案1

得分: -1

这通常在NumPy库中使用，该库提供了用于数组和矩阵的各种功能。

第一个位置的冒号符号表示应选择数组的所有行。

0:4 指定了列范围，意味着将选择索引从0到4（不包括4）的列。

使用 x[:, 0:4] 表示法，所选的子元素集将是：

[[1, 2, 3, 4],
[6, 7, 8, 9],
[11, 12, 13, 14]]

英文:

This is commonly used in the NumPy library, which provides various stuff for arrays and matrices.

The : symbol in the first position indicates that all rows of the array should be included in the selection.

The 0:4 specifies the column range and means that columns with indices from 0 up to, but not including, 4 will be selected.

x = np.array([[1, 2, 3, 4, 5],
     [6, 7, 8, 9, 10],
     [11, 12, 13, 14, 15]])

Using the x[:, 0:4] notation, the selected subset of elements would be:

[[1, 2, 3, 4],
 [6, 7, 8, 9],
 [11, 12, 13, 14]]

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