首门程序员理财课 Python量化交易系统实战

V：ititit111222333

package com.tarzan.recommend.core;

import com.tarzan.recommend.dto.RelateDTO; import org.assertj.core.util.Lists;

import java.util.*; import java.util.stream.Collectors; import java.util.stream.IntStream;

/**

核心算法
@author tarzan
@version 1.0
@company 洛阳图联科技有限公司
@date 2020/7/31 $15:21$
@since JDK1.8 */ public class CoreMath {

public List recommend(Integer userId, List list) { //找到最近邻用户id Map<Double, Integer> distances = computeNearestNeighbor(userId, list); Integer nearest = distances.values().iterator().next();
```
 Map<Integer, List<RelateDTO>>  userMap=list.stream().collect(Collectors.groupingBy(RelateDTO::getUseId));

 //最近邻用户看过电影列表
 List<Integer>  neighborItemList = userMap.get(nearest).stream().map(e->e.getModuleId()).collect(Collectors.toList());
 //指定用户看过电影列表
 List<Integer>  userItemList  = userMap.get(userId).stream().map(e->e.getModuleId()).collect(Collectors.toList());;

 //找到最近邻看过，但是该用户没看过的电影，计算推荐，放入推荐列表
 List<Integer> recommendList = new ArrayList<>();
 for (Integer item : neighborItemList) {
     if (!userItemList.contains(item)) {
         recommendList.add(item);
     }
 }
 Collections.sort(recommendList);
 return recommendList;
```
}

/**
- 在给定userId的情况下，计算其他用户和它的相关系数并排序
- @param userId
- @param list
- @return */ private Map<Double, Integer> computeNearestNeighbor(Integer userId, List list) { Map<Integer, List> userMap=list.stream().collect(Collectors.groupingBy(RelateDTO::getUseId)); Map<Double, Integer> distances = new TreeMap<>(); userMap.forEach((k,v)->{ if(k!=userId){ double distance = pearson_dis(v,userMap.get(userId)); distances.put(distance, k); } }); return distances; }
/**
- 计算两个序列间的相关系数
- @param xList
- @param yList
- @return */ private double pearson_dis(List xList, List yList) { List xs= Lists.newArrayList(); List ys= Lists.newArrayList(); xList.forEach(x->{ yList.forEach(y->{ if(x.getModuleId()==y.getModuleId()){ xs.add(x.getIndex()); ys.add(y.getIndex()); } }); }); return getRelate(xs,ys); }
/**
- 方法描述: 皮尔森（pearson）相关系数计算
- @param xs
- @param ys
- @Return {@link Double}
- @throws
- @author tarzan
- @date 2020年07月31日 17:03:20 / public static Double getRelate(List xs, List ys){ int n=xs.size(); double Ex= xs.stream().mapToDouble(x->x).sum(); double Ey=ys.stream().mapToDouble(y->y).sum(); double Ex2=xs.stream().mapToDouble(x->Math.pow(x,2)).sum(); double Ey2=ys.stream().mapToDouble(y->Math.pow(y,2)).sum(); double Exy= IntStream.range(0,n).mapToDouble(i->xs.get(i)ys.get(i)).sum(); double numerator=Exy-ExEy/n; double denominator=Math.sqrt((Ex2-Math.pow(Ex,2)/n)(Ey2-Math.pow(Ey,2)/n)); if (denominator==0) return 0.0; return numerator/denominator; }

}