hive中计算凸包面积函数

Hive中没有直接计算凸包面积的函数，但可以通过UDF来实现。

下面是一个通过Java UDF计算凸包面积的示例代码：

import java.util.List;
import java.util.ArrayList;
import org.apache.hadoop.hive.ql.exec.UDF;
import org.apache.hadoop.hive.ql.exec.Description;

@Description(name = "convex_area", value = "_FUNC_(points) - Computes the area of the convex hull of a set of points")
public class ConvexArea extends UDF {

    public double evaluate(List<String> points) {
        // Parse the input points
        List<Point> pts = new ArrayList<Point>();
        for (String point : points) {
            String[] coords = point.split(",");
            double x = Double.parseDouble(coords[0]);
            double y = Double.parseDouble(coords[1]);
            pts.add(new Point(x, y));
        }
        
        // Compute the convex hull
        List<Point> hull = convexHull(pts);
        
        // Compute the area of the convex hull
        double area = 0.0;
        int n = hull.size();
        for (int i = 0; i < n; i++) {
            Point p1 = hull.get(i);
            Point p2 = hull.get((i + 1) % n);
            area += p1.x * p2.y - p2.x * p1.y;
        }
        return Math.abs(area) / 2.0;
    }

    // Computes the convex hull of a set of points using the Graham scan algorithm
    private List<Point> convexHull(List<Point> pts) {
        // Find the point with the lowest y-coordinate
        Point minY = pts.get(0);
        for (Point pt : pts) {
            if (pt.y < minY.y) {
                minY = pt;
            }
        }

        // Sort the points by polar angle with minY
        List<Point> sortedPts = new ArrayList<Point>(pts);
        sortedPts.remove(minY);
        sortedPts.sort((p1, p2) -> {
            double angle1 = angle(minY, p1);
            double angle2 = angle(minY, p2);
            return Double.compare(angle1, angle2);
        });
        sortedPts.add(0, minY);

        // Compute the convex hull using the Graham scan algorithm
        List<Point> hull = new ArrayList<Point>();
        hull.add(sortedPts.get(0));
        hull.add(sortedPts.get(1));
        for (int i = 2; i < sortedPts.size(); i++) {
            Point p = sortedPts.get(i);
            while (hull.size() >= 2 && orientation(hull.get(hull.size() - 2), hull.get(hull.size() - 1), p) <= 0) {
                hull.remove(hull.size() - 1);
            }
            hull.add(p);
        }
        return hull;
    }

    // Computes the polar angle between two points with respect to a reference point
    private double angle(Point ref, Point pt) {
        double dx = pt.x - ref.x;
        double dy = pt.y - ref.y;
        return Math.atan2(dy, dx);
    }

    // Computes the orientation of three points (returns a positive value if they are in counterclockwise order)
    private double orientation(Point p1, Point p2, Point p3) {
        return (p2.x - p1.x) * (p3.y - p1.y) - (p2.y - p1.y) * (p3.x - p1.x);
    }

    // A simple class for representing 2D points
    private static class Point {
        public double x;
        public double y;

        public Point(double x, double y) {
            this.x = x;
            this.y = y;
        }

        public String toString() {
            return "(" + x + ", " + y + ")";
        }
    }
}

使用方法：

首先需要将上述代码编译成jar包，然后将jar包添加到Hive的classpath中：

ADD JAR /path/to/convex-area.jar;

然后可以在Hive中使用该UDF计算凸包面积：

SELECT convex_area(array("0,0", "1,2", "3,1", "2,3")) AS area;

该语句将计算坐标为(0,0)，(1,2)，(3,1)，(2,3)的点集的凸包面积。