July 2019
Intermediate to advanced
365 pages
8h 13m
Chinese
Content preview from Python机器学习手册：从数据预处理到深度学习
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1.6
对多个元素同时应用某个操作
｜
7
#
查看行数和列数
matrix.shape
(3, 4)
#
查看元素的数量（行数
*
列数）
matrix.size
12
#
查看维数
matrix.ndim
2
讨论
虽然这些操作看起来很简单（确实也是这样），但是在做下一步计算之前或在某个操作
之后，简单检查一遍数组的形状和大小是很有价值的。
1.6
对多个元素同时应用某个操作
问题描述
对一个数组中的多个元素同时应用某个函数。
解决方案
使用
NumPy
的
vecotrize
：
#
加载库
import numpy as np
#
创建一个矩阵
matrix = np.array([[1, 2, 3],
[4, 5, 6],
[7, 8, 9]])
#
创建一个函数，返回输入值加上
100
以后的值
add_100 = lambda i: i + 100
#
创建向量化函数
vectorized_add_100 = np.vectorize(add_100)
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