常用python_ML in Action

1. 

sorted:排序后影响自身

sorted(classCount.iteritems(), key=operator.itemgetter(1), reverse=True)

#按照key排序，从大到小

sort:不改变自身

argsort:返回数组从小到大的索引

2.

title(x,(datasetSize,1))

#Construct an array by repeating x the number of times given by max(reps).

3.

datasetSize = dataset.shape[0]#返回行

normDataSet = zeros(shape(dataSet))#等大的

4.

set(data)#从列表创建集合是python得到列表中唯一元素最快的方法 

5.

transpose： 对1-D array没有用，1-D matrix可以
     对2-D 转置

6.

def loadDataSet():

    dataMat = []; labelMat = []

    fr = open('testSet.txt')

    for line in fr.readlines():

        lineArr = line.strip().split()
 #strip() 删除空白符号

        dataMat.append([1.0, float(lineArr[0]), float(lineArr[1])])

        labelMat.append(int(lineArr[2]))

    return dataMat,labelMat

7.

mat1 = dataSet[nonzero(dataSet[:,feature] <= value)[0],:][0]

#返回值不为0的下标，默认返回两维，横的竖的

############plot

1.

from numpy import *

import matplotlib

import matplotlib.pyplot as plt

fig = plt.figure()

ax = fig.add_subplot(111)

#datingDataMat,datingLabels = file2matrix('datingTestSet.txt')

#ax.scatter(datingDataMat[:,1], datingDataMat[:,2])

ax.scatter(datingDataMat[:,1], datingDataMat[:,2], 15.0*array(datingLabels), 15.0*array(datingLabels))#为两个类进行颜色标注

ax.axis([-2,25,-0.2,2.0])

plt.xlabel('Percentage of Time Spent Playing Video Games')

plt.ylabel('Liters of Ice Cream Consumed Per Week')

plt.show()

2.

annotation:画图注解工具