ADD file via upload

flower_back/src/main/java/com/example/flower/unit/CoreMath.java

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+package com.example.flower.unit;
+
+import cn.hutool.core.collection.CollectionUtil;
+import com.example.flower.entity.RelateDTO;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Map;
+import java.util.TreeMap;
+import java.util.stream.IntStream;
+
+public class CoreMath {
+    /**
+     * 计算相关系数并排序
+     */
+    public static Map<Integer, Double> computeNeighbor(Integer key, Map<Integer, List<RelateDTO>> map, int type) {
+        Map<Integer, Double> distMap = new TreeMap<>();
+        List<RelateDTO> userItems = map.get(key);
+        if (CollectionUtil.isNotEmpty(userItems)) {
+            map.forEach((k, v) -> {
+                //排除此用户
+                if (!k.equals(key)) {
+                    //关系系数
+                    double coefficient = relateDist(v, userItems, type);
+                    //关系距离
+                    double distance = Math.abs(coefficient);
+                    distMap.put(k, distance);
+                }
+            });
+        }
+        return distMap;
+    }
+
+
+    /**
+     * 计算两个序列间的相关系数
+     */
+    private static double relateDist(List<RelateDTO> xList, List<RelateDTO> yList, int type) {
+        List<Integer> xs = new ArrayList<>();
+        List<Integer> ys = new ArrayList<>();
+        xList.forEach(x -> yList.forEach(y -> {
+            if (type == 0) {
+                if (x.getGoodsId().equals(y.getGoodsId())) {
+                    xs.add(x.getIndex());
+                    ys.add(y.getIndex());
+                }
+            } else {
+                if (x.getUseId().equals(y.getUseId())) {
+                    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 x集合
+     * @param ys y集合
+     * @Return {@link double}
+     */
+    public static double getRelate(List<Integer> xs, List<Integer> ys) {
+        int n = xs.size();
+        //至少有两个元素
+        if (n < 2) {
+            return 0D;
+        }
+        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 - Ex * Ey / n;
+        double denominator = Math.sqrt((Ex2 - Math.pow(Ex, 2) / n) * (Ey2 - Math.pow(Ey, 2) / n));
+        if (denominator == 0) {
+            return 0D;
+        }
+        return numerator / denominator;
+    }
+
+}