优化：一种将grid-search速度提升10倍的方法

Python 2.7
IDE Pychrm 5.0.3
sci-kit learn 0.18.1

前言

抖了个机灵，不要来打我，这是没有理论依据证明的，只是模型测试出来的确有效，并且等待时间下降(约)为原来的十分之一！！刺不刺激，哈哈哈。

原理

基本思想：先找重点在细分，再细分，伸缩Flexible你怕不怕。以下简称这种方法为FCV

不知道CV的请看@MrLevo520–总结：Bias(偏差)，Error(误差)，Variance(方差)及CV(交叉验证)

伪代码

原理很好理解，直接上伪代码，懒得打字，上手稿

FCV测试时间

以GBDT为例，我测试了下，参数 n_estimators从190到300，max_depth从2到9，CV=3

普通的GridSerachCV总共fit了110*7*3=2310次，耗时1842min，也就是30.7个小时，得出最优参数n_estimators=289，max_depth=3
FCV总共总共fit了345次，跑了166min，也就是2.8小时，得出最优参数n_estimators=256，max_depth=3

时间方面，相差11倍，那么效果呢，请看下面的CV得分

FCV测试效果

选取了GBDT,RF,XGBOST,SVM做了交叉验证比较，同一算法之间保持相同参数。

GBDT的测试结果

clf1 = GradientBoostingClassifier(max_depth=3,n_estimators=289)#.fit(train_data,train_label)
score1 = model_selection.cross_val_score(clf1,train_data,train_label,cv=5)
print score1
-------------------------------------
clf2 = GradientBoostingClassifier(max_depth=3,n_estimators=256)#.fit(train_data,train_label)
score2 = model_selection.cross_val_score(clf2,train_data,train_label,cv=5)
print score2------------------------------------
# 查看两种方法的交叉验证效果#传统方法CV=5：[ 0.79807692  0.82038835  0.80684597  0.76108374  0.78163772]
#改进方法CV=5：[ 0.79567308  0.82038835  0.799511    0.76847291  0.78411911]---------------------------------------#传统方法CV=10:[ 0.83333333  0.78571429  0.84615385  0.7961165   0.81067961  0.80097087   0.77227723  0.78109453  0.785   0.74111675]
#FCV方法CV=10:[ 0.85238095  0.78095238  0.85096154  0.7961165   0.81553398  0.7961165   0.76732673  0.79104478  0.795   0.75126904]

Xgboost的测试结果

clf1 = XGBClassifier(max_depth=6,n_estimators=200)#.fit(train_data,train_label)
score1 = model_selection.cross_val_score(clf1,train_data,train_label,cv=5)
print score1clf2 = XGBClassifier(max_depth=4,n_estimators=292)#.fit(train_data,train_label)
score2 = model_selection.cross_val_score(clf2,train_data,train_label,cv=5)
print score2-----------------------------
#传统方法CV=5：[ 0.79086538  0.83737864  0.80929095  0.79310345  0.7866005 ]
#FCV方法CV=5：[ 0.80288462  0.84466019  0.8190709   0.79064039  0.78163772]

RF的测试结果

注：由于RF的特殊性，选择样本的方式和选择特征的方式都随机，所以即使交叉验证，效果也不是稳定的，就像我在服务器上跑多进程和笔记本上跑同一个程序，出来的最佳值一个是247，一个是253，并不是说都会一致。(说的好像GBDT,XGBOOST不是树结构似得0.o)

clf1 = RandomForestClassifier(n_estimators=205)#.fit(train_data,train_label)
score1 = model_selection.cross_val_score(clf1,train_data,train_label,cv=5)
print score1
clf2 = RandomForestClassifier(n_estimators=253)#.fit(train_data,train_label)
score2 = model_selection.cross_val_score(clf2,train_data,train_label,cv=5)
print score2---------------
#传统方法CV=5: [ 0.77884615  0.82038835  0.78239609  0.79310345  0.74937965]
#FCV方法CV=5：[ 0.75721154  0.83495146  0.79217604  0.79310345  0.75186104]

SVM的测试结果

clf1 = SVC(kernel='rbf', C=16, gamma=0.18)#.fit(train_data,train_label)
score1 = model_selection.cross_val_score(clf1,train_data,train_label,cv=5)
print score1clf2 = SVC(kernel='rbf', C=94.75, gamma=0.17)#.fit(train_data,train_label)
score2 = model_selection.cross_val_score(clf2,train_data,train_label,cv=5)
print score2# 默认CV参数搜索(2^-8，2^8)，[ 0.88468992  0.88942774  0.88487805  0.8856305   0.8745098 ]# FCV参数搜索：[ 0.90116279  0.9185257   0.90146341  0.90713587  0.89509804]

FCV优点

分割测试阈，极大提高速度，相较于普通的寻优，速度提升Step倍左右，寻优范围越大，提升越明显
可根据自己的数据集进行弹性系数设置，默认为0.5Step，设置有效的弹性系数有利于减少遗漏值

FCV缺点

有一定几率陷入局部最优
需要有一定的阈值经验和步进Step设置经验

FCV代码

以GBDT为例，(RF被我改成多进程了),假设寻找两个最优参数，概念和上面的是一样的，上面的理解了，这里没啥问题的。

# -*- coding: utf-8 -*-
from sklearn import metrics, model_selection
import LoadSolitData
import Confusion_Show as cs
from sklearn.model_selection import GridSearchCV
from sklearn.ensemble import GradientBoostingClassifierdef gradient_boosting_classifier(train_x, train_y,Nminedge,Nmaxedge,Nstep,Dminedge,Dmaxedge,Dstep):model = GradientBoostingClassifier()param_grid = {'n_estimators': [i for i in range(Nminedge,Nmaxedge,Nstep)], 'max_depth': [j for j in range(Dminedge,Dmaxedge,Dstep)]}grid_search = GridSearchCV(model, param_grid, n_jobs=1, verbose=1)grid_search.fit(train_x, train_y)best_parameters = grid_search.best_estimator_.get_params()for para, val in best_parameters.items():print para, valreturn best_parameters["n_estimators"],best_parameters["max_depth"]def FlexSearch(train_x, train_y,Nminedge,Nmaxedge,Nstep,Dminedge,Dmaxedge,Dstep):NmedEdge,DmedEdge = gradient_boosting_classifier(train_x, train_y,Nminedge,Nmaxedge,Nstep,Dminedge,Dmaxedge,Dstep)Nminedge = NmedEdge - Nstep-Nstep/2Nmaxedge = NmedEdge + Nstep+Nstep/2Dminedge = DmedEdge - DstepDmaxedge = DmedEdge + DstepNstep = Nstep/2Dstep = Dstepprint "Current bestPara:N-%.2f,D-%.2f"%(NmedEdge,DmedEdge)print "Next Range:N-%d-%d,D--%d-%d"%(Nminedge,Nmaxedge,Dminedge,Dmaxedge)print "Next step:N-%.2f,D-%.2f"%(Nstep,Nstep)if Nstep > 0 :return FlexSearch(train_x, train_y,Nminedge,Nmaxedge,Nstep,Dminedge,Dmaxedge,Dstep)else:print "The bestPara:N-%.2f,D-%.2f"%(NmedEdge,DmedEdge)return NmedEdge,DmedEdgeif __name__ == '__main__':train_data,train_label,test_data,test_label = LoadSolitData.TrainSize(1,0.2,[i for i in range(1,14)],"outclass")
#这里数据自己导，我是写在别的子函数里面了。NmedEdge,DmedEdge = FlexSearch(train_data, train_label, 190, 300, 10, 2, 9, 1)Classifier = GradientBoostingClassifier(n_estimators=NmedEdge,max_depth=DmedEdge)Classifier.fit(train_data,train_label)predict_label = Classifier.predict(test_data)report = metrics.classification_report(test_label, predict_label)print report

What’s More

采用多进程+FCV的方法，速度再次提升一个数量级。我假定命名为MFCV方法

不知道什么是多进程和多线程请看
@MrLevo520–Python小白带小白初涉多进程
@MrLevo520–Python小白带小白初涉多线程

MFCV原理

在FCV的基础上，gap = (maxedge-minedge)/k，其中的k为进程个数，把大块切割成小块，然后小块在按照FCV进行计算，最后得出K个最优值，再进行K个最优值选择一下就可以了。

MFCV优点

速度更快，多进程并发
因为分割片在片上做FCV,然后再集合做CV,一定程度上避免FCV陷入局部最优

MFCV缺点

与FCV不同，只能进行单参数的多进程并发寻优，两个参数的现在多进程我还没想到怎么实现，想到再说。

MFCV测试时间

因为只能单参数，所以RF为例，参数 n_estimators从190到330，CV=10，普通GridSerachCV时间为97.2min，而FCV时间为18min，MFCV为14min，这里因为fit总数太少了，所以效果不是非常明显，但是大家可以想象一下，单参数跨度很大的时候是什么效果。。。

MFCV测试效果

clf1 = RandomForestClassifier(n_estimators=205)#.fit(train_data,train_label)
score1 = model_selection.cross_val_score(clf1,train_data,train_label,cv=10)
print score1
clf2 = RandomForestClassifier(n_estimators=239)#.fit(train_data,train_label)
score2 = model_selection.cross_val_score(clf2,train_data,train_label,cv=10)
print score2#传统方法CV=10：[ 0.84169884  0.85328185  0.85907336  0.84912959  0.82101167  0.8540856 0.84015595  0.87968442  0.84980237  0.83003953]
#MFCV方法CV=10：[ 0.84169884  0.86100386  0.85521236  0.86266925  0.82101167  0.85019455  0.83625731  0.87771203  0.85177866  0.83201581]

效果和传统方法相比，相差不多，持平，并且速度提升一个数量集，我认为可以采用

MFCV代码

# -*- coding: utf-8 -*-
#! /usr/bin/python
from multiprocessing import Process
from sklearn.ensemble import RandomForestClassifier
from sklearn import metrics
import Confusion_Show as cs
import LoadSolitData
from sklearn.model_selection import GridSearchCVdef write2txt(data,storename):f = open(storename,"w")f.write(str(data))f.close()def V_candidate(candidatelist,train_x, train_y):model = RandomForestClassifier()param_grid = {'n_estimators': [i for i in candidatelist]}grid_search = GridSearchCV(model, param_grid, n_jobs=1, verbose=1,cv=10)grid_search.fit(train_x, train_y)best_parameters = grid_search.best_estimator_.get_params()for para, val in best_parameters.items():print para, valreturn best_parameters["n_estimators"]def random_forest_classifier(train_x, train_y,minedge,maxedge,step):model = RandomForestClassifier()param_grid = {'n_estimators': [i for i in range(minedge,maxedge,step)]}grid_search = GridSearchCV(model, param_grid, n_jobs=1, verbose=1,cv=10)grid_search.fit(train_x, train_y)best_parameters = grid_search.best_estimator_.get_params()for para, val in best_parameters.items():print para, valreturn best_parameters["n_estimators"]def FlexSearch(train_x, train_y,minedge,maxedge,step,storename):mededge = random_forest_classifier(train_x, train_y,minedge,maxedge,step)minedge = mededge - step-step/2maxedge = mededge + step+step/2step = step/2print "Current bestPara:",mededgeprint "Next Range%d-%d"%(minedge,maxedge)print "Next step:",stepif step > 0:return FlexSearch(train_x, train_y,minedge,maxedge,step,storename)elif step==0:print "The bestPara:",mededgewrite2txt(mededge,"RF_%s.txt"%storename)def Calc(classifier):Classifier.fit(train_data,train_label)predict_label = Classifier.predict(test_data)predict_label_prob = Classifier.predict_proba(test_data)total_cor_num = 0.0dictTotalLabel = {}dictCorrectLabel = {}for label_i in range(len(predict_label)):if predict_label[label_i] == test_label[label_i]:total_cor_num += 1if predict_label[label_i] not in dictCorrectLabel: dictCorrectLabel[predict_label[label_i]] = 0dictCorrectLabel[predict_label[label_i]] += 1.0if test_label[label_i] not in dictTotalLabel: dictTotalLabel[test_label[label_i]] = 0dictTotalLabel[test_label[label_i]] += 1.0accuracy = metrics.accuracy_score(test_label, predict_label) * 100kappa_score = metrics.cohen_kappa_score(test_label, predict_label)average_accuracy = 0.0label_num = 0for key_i in dictTotalLabel:try:average_accuracy += (dictCorrectLabel[key_i] / dictTotalLabel[key_i]) * 100label_num += 1except:average_accuracy = average_accuracyaverage_accuracy = average_accuracy / label_numresult = "OA:%.4f;AA:%.4f;KAPPA:%.4f"%(accuracy,average_accuracy,kappa_score)print resultreport = metrics.classification_report(test_label, predict_label)print reportcm = metrics.confusion_matrix(test_label, predict_label)cs.ConfusionMatrixPng(cm,['1','2','3','4','5','6','7','8','9','10','11','12','13'])if __name__ == '__main__':train_data,train_label,test_data,test_label = LoadSolitData.TrainSize(1,0.5,[i for i in range(1,14)],"outclass") # 数据集自导自己的minedge = 180maxedge = 330step = 10gap = (maxedge-minedge)/3subprocess = []for i in range(1,4):#设置了3个进程p = Process(target=FlexSearch,args=(train_data,train_label,minedge+(i-1)*gap,minedge+i*gap,step,i))subprocess.append(p)for j in subprocess:j.start()for k in subprocess:k.join()candidatelist = []for i in range(1,4):with open("RF_%s.txt"%i) as f:candidatelist.append(int(f.readlines()[0].strip()))print "candidatelist:",candidatelistbest_n_estimators = V_candidate(candidatelist, train_data,train_label)print "best_n_estimators",best_n_estimatorsClassifier = RandomForestClassifier(n_estimators=best_n_estimators)Calc(Classifier)

总结

在单参数寻优上可以选用MFCV,多参数寻优上选择FCV，经过CV得分可知，效果与普通遍历查询保持一致，但是速度提升效果明显，越是广阈查询，提升越明显，已通过ISO9001认证，请放心食用。。。。。。算法非常简单啊，但万一哪天火了呢，所以我要保留所有权利，转载请注明。（我能说Bootstrap这么简单的一种思想是怎么统治统计学的么，BTW，GridSerach思想本来也很简单呢）

附录1–FCV手稿

手稿1

手稿2

附录2

如果你也想尝试xgboost这个非常好用的分类器，强烈建议你采用FCV进行调参，因为xgboost借助OpenMP，能自动利用单机CPU的多核进行并行计算，就像这样，一运行就陷入烤鸡模式，所以尽量减少调参时候的运行次数极为重要！

如何安装Xgboost请看@MrLevo520–解决：win10_x64 xgboost python安装所遇到问题

致谢

@abcjennifer–python并行调参——scikit-learn grid_search
@MrLevo520–解决：win10_x64 xgboost python安装所遇到问题 @wzmsltw–XGBoost-Python完全调参指南-参数解释篇
@u010414589–xgboost 调参经验
@MrLevo520–总结：Bias(偏差)，Error(误差)，Variance(方差)及CV(交叉验证)
@MrLevo520–Python小白带小白初涉多进程
@MrLevo520–Python小白带小白初涉多线程