Integration of Rules from a Random Forest

Transcription

1 2011 Internatonal Conference on Informaton and Electroncs Engneerng IPCSIT vol.6 (2011) (2011) IACSIT Press, Sngapore Integraton of Rules from a Random Forest Naphaporn Srkulvrya 1 and Sukree Snthupnyo 2 1 Department of Computer Engneerng, Chulalongkorn Unversty, Bangkok, Thaland E-mal: naphaporn.s@student.chula.ac.th 2 Department of Computer Engneerng, Chulalongkorn Unversty, Bangkok, Thaland E-mal: sukree.s@chula.ac.th Abstract. Random forests s an effectve predcton tool wdely used n data mnng. However, the usage and human comprehensveness of the rules obtaned from a forest s a dffcult task because of an amount of rules, whch are patterns of the data, from a number of trees. Moreover, some rules conflct wth other rules. Ths paper thus proposes a new method whch can ntegrate rules from multple trees n a Random Forest whch can help mprove the comprehensveness of the rules. The experments show that the rules obtaned from our method yelded the better results and also reduced the nconsstent condton between rules from dfferent decson trees n the same forest. Keywords: Random Forests, rules ntegraton, Decson Trees. 1. Introducton Ensemble method s a popular machne learnng technque whch has been nterested n data mnng communtes. It s wdely accepted that the accuracy from the ensemble of several weak classfers s usually better than a sngle classfer gven the same amount of tranng nformaton. A number of effectve ensemble algorthms have been nvented durng the past 15 years, such as Baggng (Breman, 1996), Boostng (Freund and Schapre, 1996), Archng (Breman, 1998) and Random Forests (Breman, 2001). Random Forests [1] s an ensemble classfer proposed by Breman. It constructs a seres of classfcaton trees whch wll be used to classfy a new example. The dea used to create a classfer model s constructng multple decson trees, each of whch uses a subset of attrbutes randomly selected from the whole orgnal set of attrbutes. However, the rules generated by exstng ensemble technques sometmes conflct wth the rules generated from another classfer. Ths may lead to a problem when we want to combne all rule set nto a sngle rule set. Therefore, several works ntend to ncrease the accuracy of the classfers. In ths paper, we present an approach whch can ntegrate rules from multple decson trees. Our method s amed at ncrementally ntegratng a par of rules. The newly ntegrated rules wll replace ts orgnal rules. The replacement process wll be repeated untl a stoppng crteron s met. Fnally, the new set of rules wll be used to classfy a new data. 2. Random Forests The Random Forests [1] s an effectve predcton tool n data mnng. It employs the Baggng method to produce a randomly sampled set of tranng data for each of the trees. Ths Random Forests method also sem-randomly selects splttng features; a random subset of a gven sze s produced from the space of possble splttng features. The best splttng s feature determnstcally selected from that subset. A pseudo code of random forest constructon s shown n Fgure 1. To classfy a test nstance, the Random Forests classfes the nstance by smply combnng all results from each of the trees n the forest. The method used to combne the results can be as smple as predctng the class obtaned from the hghest number of trees. 194

2 Algorthm 1: Pseudo code for the random forest algorthm To generate c classfers: for = 1 to c do Randomly sample the tranng data D wth replacement to produce Create a root node, Call BuldTree( N ) end for N contanng D BuldTree(N): f N contans nstances of only one class then return else Randomly select x% of the possble splttng features n N Select the feature F wth the hghest nformaton gan to splt on Create f chld nodes of N, N 1,..., N f, where F has f possble values ( F 1,, for = 1 to f do Set the contents of N to D, where D s all nstances n N that match F Call BuldTree( N ) end for end f D F ) f 3. Methodology Fg. 1: The pseudo code of Random Forest algorthm [17] 3.1. Extractng Rules from Decson Tree A method for extractng rules from a decson tree [11] s qute smple. A rule can be extracted from a path lnkng from the root to a leaf node. All nodes n the path are gathered and connected to each other usng conjunctve operatons. Fg. 2: An example of decson tree For example, a decson tree for classfyng the person who get sunburned after sunbathe s shown n Fg. 2. A rule of sunburned person can be obtaned from the root node har color and ts value blonde lnkng to the node loton used and ts value no. So that the extracted rule wll be IF har color s blonde and loton used s no, THEN sunburned. All obtaned rules from the tree n Fg. 2 are lsted below. (1) IF har color s blonde AND loton used s no THEN nothng happens. (2) IF har color s blonde AND loton used s yes THEN the person gets sunburned. (3) IF har color s red THEN the person gets sunburned (4) IF har color s brown THEN nothng happens 3.2. Integraton of Rules from Random Forests 195

3 We have proposed a new method to ntegrate rules from random forests whch has the followng steps. 1. Remove redundancy condtons In ths step, we wll remove the more general condtons whch appear n the same rule wth more specfc condtons. For example: IF weght>40 AND weght>70 AND weght>80 AND weght<150 AND heght<180 THEN fgure=fat We can see that the condton weght>80 s more specfc than weght>40 and weght>70 so weght>40 and weght>70 are removed. The fnal rule wll be IF weght>80 AND weght<150 AND heght<180 THEN fgure=fat 2. For every par decson trees 2.1 Remove redundancy rules. For example: Rule 1: IF thckness=thn AND lace=glue THEN report=mnor Rule 2: IF thckness=thn AND lace=glue THEN report=mnor New Rule: IF thckness=thn AND lace=glue THEN report=mnor 2.2 Remove all conflcts rules. The rules wth the same condtons but dfferent consequences must be removed. For example: Rule 1: IF face=soft AND age>3 THEN toy=doll Rule 2: IF face=soft AND age>3 THEN toy=elastc New Rule: Remove more specfc rules. The rules wth a condton set whch s a superset of another rule should be removed. For example: Rule 1: IF fur=short AND nose=yes AND tal=yes THEN type=bear Rule 2: IF fur=short AND ear=yes AND nose=yes AND tal=yes THEN type=bear Rule 3: IF nose=yes AND tal=yes THEN type=bear New Rule: IF nose=yes AND tal=yes THEN type=bear 2.4 Extend the range of contnuous condtons. The rules wth the range of the same attrbute can be combned nto the wdest one. For example: Rule 1: IF duty=recordng AND perod<3 AND perod>1.5 THEN wage=1500 Rule 2: IF duty=recordng AND perod<2 AND perod>1 THEN wage=1500 New Rule: IF duty=recordng AND perod<3 AND perod>1 THEN wage= Dvde range of condtons. The rules of dfferent classes wth the same attrbute whch has overlapped range should be dvded nto several parts. For example: Rule 1: IF credt=yes AND money>20000 THEN allow=yes Rule 2: IF credt=yes AND money<40000 THEN allow=no New Rule 1: IF credt=yes AND money>=40000 THEN allow=yes New Rule 2: IF credt=yes AND money<=20000 THEN allow=no Rule 3: IF usage>100 AND payment=pad THEN promoton=false Rule 4: IF usage>=200 AND usage<400 AND payment=pad THEN promoton=true 196

4 New Rule 3: IF usage>100 AND usage<200 AND payment=pad THEN promoton=false New Rule 4: IF usage>=200 AND usage<400 AND payment=pad THEN promoton=true New Rule 5: IF usage>=400 AND payment=pad THEN promoton=false 2.6 If percent of accuracy of new rules on the valdaton set s stll mproved, repeat Output the new rule set 4. Experments 4.1. Data Sets We used seven datasets from UCI Machne Learnng Repostory [15], namely Balance Scale, Blood Transfuson, Haberman's Survval, Irs, Lver Dsorders, Pma Indans Dabetes Database, and Statlog. Moreover, we compared our proposed method to Random Forests and C4.5 [7] usng a standard 10-fold Cross Valdaton. In each tranng set, a valdaton set whch was used to fnd the best new rule set conssted of 20% of the number of tranng examples n the orgnal tranng set. The remanng was used to tran a Random Forest. In ths experment, we used WEKA [14] as our learnng tool Expermental Results Because the order of the rules whch are ntegrated can affect the fnal results, we dvded our rule ntegraton method nto two ways,.e. ntegrate the hghest accurate rule frst (RFh) and ntegrate the lower accurate rule frst (RFl). The results obtaned from our experments are shown n Table 1. Accuracy (%) Data Set Random RFh RFl Forests C4.5 Balance Scale Blood Transfuson Haberman's Survval Irs Lver Dsorders Pma Indans Dabetes Database Statlog Table1. The average of accuracy percent of predctng result by ntegratng rules compare wth Random Forest and C Concluson We have been proposed a new method whch can ntegrate rules obtaned from several trees n a Random Forest. The results from seven datasets from UCI machne learnng repostory show that our method yelds the better classfcaton results than the orgnal random forest and the ordnary decson tree. Moreover, the rule set from our ntegraton method can help users when they use the rule set. The rules from dfferent decson trees may conflct wth rules from another tree. Our method can remove these nconsstent condtons and output a new rule set whch can be better appled to classfy unseen data. 6. Acknowledgements Ths work was supported by the Thaland Research Fund (TRF). 7. References [1] L. Breman. Random Forests. Machne Learnng, 45(1):5-32,

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