November 2023
Intermediate to advanced
512 pages
11h 53m
Chinese
Content preview from 利用 Python 进行数据分析：原书第 3 版
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高阶
NumPy
|
451
A.2.5
花式索引的等价方法：
take
和
put
第
4
章讲过，获取和设置数组子集的办法之一是通过整数数组使用花式索引：
对于在单个轴向上进行选取这种特殊情况，
ndarray
还有其他方法：
要在其他轴上使用 take，只需传入关键字 axis 即可：
put 不接收参数 axis，它只会在数组的扁平化（一维，
C
顺序）版本上进行索引。因此，
在需要用其他轴向的索引设置元素时，最好还是使用花式索引。
A.3
广播
广播机制指的是不同形状数组之间的算术运算执行方式。这是一种非常强大的功能，但
452
|
附录
A
也容易令人误解，即使是经验丰富的老手也是如此。标量值和数组的运算是最简单的广
播示例：
在这个乘法运算中，标量值
4
被广播到了其他所有元素上。
看一个例子，我们可以通过减去列平均值的方式，降低数组中每一列的数值。对于这种
情况，只能通过减去包含各列平均值的数组来实现：
图
A-4
形象地展示了该操作过程。用广播的方式对行减去均值时需要特别留心。幸运的
是，只要遵循一定的规则，低维度的值是可以被广播到数组的任意维度的（比如对二维
数组各列减去行平均值）。
于是就得到了广播机制。
广播机制
如果两个数组的后缘维度（即从末尾开始算起的维度）的轴长度相符或其中一方
的长度为 1，则这两个数组是广播兼容的。广播会在缺失维度或长度为 ...
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I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.