數據預處理-采樣

采樣就是按照某種規則從數據集中挑選樣本數據，大致分為3類：隨機采樣、系統采樣和分層采樣。

隨機采樣：就是從數據集中隨機的抽取特定數量的數據，分為有放回和無放回兩種。

import random

def noRepetRandomSampling(dataMat,number):
    '''
    無放回采樣
    :param dataMat: 數據集
    :param number: 采樣數
    :return: sample 采樣到的數據
    '''
    try:
        length = len(dataMat)
        sample = random.sample(dataMat, number)
        return sample
    except Exception as e:
        print(e)

def repetRandomSampling(dataMat,number):
    '''
    有放回采樣
    :param dataMat: 數據集
    :param number: 采樣數
    :return: sample 采樣到的數據
    '''
    sample = []
    i = 0
    while(i<number):
        sample.append(dataMat[random.randint(0,len(dataMat)-1)])  #randint的范圍是a<=x<=b，包括上限，注意要減一
        i+=1
    return sample

系統采樣：一般是無放回抽樣，又稱等距采樣，先將總體數據集按順序分成n小份，再從每小份抽取第k個數據。

import random

def systemSampling(dataMat,number):
    '''
    系統采樣
    :param dataMat: 數據集
    :param number: 采樣數
    :return: sample 采樣到的數據
    '''
    length=len(dataMat)
    k=int(length/number)
    sample=[]
    i=0
    if k>0:
        while (i<number):
            sample.append(dataMat[0+i*k])
            i+=1
        return sample
    else:
        return repetRandomSampling(dataMat,number)

分層采樣：就是先將數據分成若干個類別，再從每一層內隨機抽取一定數量的樣本，然后將這些樣本組合起來。

import random

def stratifiedSampling(dataMat1,dataMat2,dataMat3,number):
    '''
    分層采樣
    :param dataMat1: 數據集1
    :param dataMat2: 數據集2
    :param dataMat3: 數據集3
    :param number: 采樣數
    :return: sample 采樣到的數據
    '''
    subNumber=int(number/3)
    sample=[]
    sample.append(noRepetRandomSampling(dataMat1,subNumber))
    sample.append(noRepetRandomSampling(dataMat2,subNumber))
    sample.append(noRepetRandomSampling(dataMat3,subNumber))
    return sample

 測試代碼：

dataMat=[1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20]
dataMat1=[101,102,103,104,105,106,107,108,109,110]
dataMat2=[201,202,203,204,205,206,207,208,209,210]
dataMat3=[301,302,303,304,305,306,307,308,309,310]

print(repetRandomSampling(dataMat,6))
print(noRepetRandomSampling(dataMat,6))
print(systemSampling(dataMat,6))
print(stratifiedSampling(dataMat1,dataMat2,dataMat3,6))

運行結果：

E:\Anaconda3\python.exe E:/數據采樣.py
[8, 1, 8, 13, 19, 3]
[14, 8, 5, 1, 17, 16]
[1, 4, 7, 10, 13, 16]
[[108, 105], [201, 208], [301, 308]]

 

以上內容摘自《機器學習實踐應用》