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