numpy是学习数据分析和人工智能必不可少的库,大量的计算方法在numpy中都有现成的方法,下面介绍其常用的方法
- numpy替换值
如下:替换矩阵中的空字符串
#!usr/bin/python3
import numpy as np
matrix = np.array([[5, 10, 15], [20, 25, 30], [35, 40, '']])
second_column = matrix[:, 2] == ''
matrix[second_column, 2] = 0
print("matrix = ", matrix)
结果:
matrix = [[‘5′ ’10’ ’15’]
[’20’ ’25’ ’30’]
[’35’ ’40’ ‘0’]]
- 改变类型
#!usr/bin/python3
import numpy as np
vector = np.array(["1", "2", "3"])
vector = vector.astype(float) # 将字符串类型改变为float类型
print("vector = ", vector)
结果:
vector = [1. 2. 3.]
- numpy的统计计算方法
3.1 计算总和
3.1.1 向量计算总和(一位数组)
#!usr/bin/python3
import numpy as np
vector = np.array([5, 10, 15, 20])
print("sum = ", vector.sum())
结果:
sum = 50
3.1.2 矩阵计算总和(二位数组)
矩阵计算总和的话,要分按行还是按列axis=0表示按列计算,结果用行表示,axis=1表示按行计算,结果用列表示
#!usr/bin/python3
import numpy as np
matrix = np.array([[1, 2, 3], [4, 5, 6], [7, 8, 9]])
print("sum = ", matrix.sum(axis=0))
结果:
sum = [12 15 18]
#!usr/bin/python3
import numpy as np
matrix = np.array([[1, 2, 3], [4, 5, 6], [7, 8, 9]])
print("sum = ", matrix.sum(axis=1))
结果:
sum = [ 6 15 24]
Original: https://blog.csdn.net/qq_24430629/article/details/124423250
Author: 愿乘长风、破万里浪
Title: 第一章 Numpy
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