使用Streams实现Java Pivot表

Question

我几天来一直在努力解决这个问题.我正在尝试使用Java Streams创建Pivot功能.我只需要实现SUM,COUNT,MAX,MIN和AVERAGE.对于输入,我给出了一个Pivot Column Index,一个pivot行索引数组和要计算的值.

catch是数据在List <List <Object >>中,Where对象是String,Integer或Double.但直到运行时我才知道.我必须将结果作为List <List <Object >>返回.

我在使用MAX/MIN时遇到问题(我假设AVERAGE与MAX和MIN类似)

为了在多个表值上进行数据透视,我创建了一个类来使用我的第二个groupingBy

这不会编译,我不知道要比较什么,将对象转换为int或者如果我甚至需要.我想用一个流来做这一切,但我不确定它是否可行.我做错了什么,或者我可以做不同的事情.提前致谢.

package pivot.test;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;
import java.util.Map;
import java.util.Optional;
import java.util.stream.Collectors;

public class PivotTest {

    List<List<Object>> rows = new ArrayList<List<Object>>();

    public PivotTest() throws Exception {

        rows.add(Arrays.asList(new Object[]{ "East", "Boy", "Tee", 10, 12.00}));
        rows.add(Arrays.asList(new Object[]{ "East", "Boy", "Golf", 15, 20.00}));
        rows.add(Arrays.asList(new Object[]{ "East", "Girl", "Tee", 8, 14.00}));
        rows.add(Arrays.asList(new Object[]{ "East", "Girl", "Golf", 20, 24.00}));
        rows.add(Arrays.asList(new Object[]{ "West", "Boy", "Tee", 5, 12.00}));
        rows.add(Arrays.asList(new Object[]{ "West", "Boy", "Golf", 12, 20.00}));
        rows.add(Arrays.asList(new Object[]{ "West", "Girl", "Tee", 15, 14.00}));
        rows.add(Arrays.asList(new Object[]{ "West", "Girl", "Golf", 10, 24.00}));

    }

    // Dynamic Max based upon Column, Value to sum, and an array of pivot rows
    public void MaxTable(int colIdx, int valueIdx, int... rowIdx) {

         Map<Object, Map<Object, Integer>> myList = newRows.stream().collect(
         Collectors.groupingBy(r -> ((List<Object>) r).get(colIdx),
         Collectors.groupingBy( r -> new PivotColumns(r, rowIdx),
         Collectors.collectingAndThen( Collectors.maxBy(Comparator.comparingInt(???)),
                r -> ((List<Object>) r).get(valueIdx)))));

         System.out.println("Dynamic MAX PIVOT"); System.out.println(myList);

    }

    public static void main(String[] args) {

        try {
            PivotTest p = new PivotTest();
            System.out.println("\n\nStreams PIVOT with index values inside a List\n");
            p.MaxTable(0, 3, new int[] { 2 });
        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }

}

class PivotColumns {

    ArrayList<Object> columns;

    public PivotColumns(
        List<Object> objs, int... pRows) {
        columns = new ArrayList<Object>();

        for (int i = 0; i < pRows.length; i++) {
            columns.add(objs.get(pRows[i]));
        }

    }

    public void addObject(Object obj) {
        columns.add(obj);
    }

    @Override
    public int hashCode() {
        final int prime = 31;
        int result = 1;
        result = prime * result + ((columns == null) ? 0 : columns.hashCode());
        return result;
    }

    @Override
    public boolean equals(Object obj) {
        if (this == obj)
            return true;
        if (obj == null)
            return false;
        if (getClass() != obj.getClass())
            return false;
        PivotColumns other = (PivotColumns) obj;
        if (columns == null) {
            if (other.columns != null)
                return false;
        } else if (!columns.equals(other.columns))
            return false;
        return true;
    }

    public String toString() {
        String s = "";
        for (Object obj : columns) {
            s += obj + ",";
        }

        return s.substring(0, s.lastIndexOf(','));
    }

}

Answer 1

由于所有可能的值 ( String、Integer、Double) 已知为Comparable，因此您可以对接口执行未经检查的强制转换Comparable。另外不要忘记打开可选的包装。最后，如果我理解正确，结果应该是Map<Object, Map<Object, Object>> myList，而不是Map<Object, Map<Object, Integer>> myList，因为您的列可能有非整数值：

public void MaxTable(int colIdx, int valueIdx, int... rowIdx) {
     Map<Object, Map<Object, Object>> myList = newRows.stream().collect(
     Collectors.groupingBy(r -> r.get(colIdx),
     Collectors.groupingBy( r -> new PivotColumns(r, rowIdx),
     Collectors.collectingAndThen( Collectors.maxBy(
         Comparator.comparing(r -> (Comparable<Object>)(((List<Object>) r).get(valueIdx)))),
         r -> r.get().get(valueIdx)))));

     System.out.println("Dynamic MAX PIVOT"); System.out.println(myList);
}

结果：

> p.MaxTable(0, 3, new int[] { 1 });
{West={Girl=15, Boy=12}, East={Girl=20, Boy=15}}

> p.MaxTable(0, 4, new int[] { 1 });
{West={Girl=24.0, Boy=20.0}, East={Girl=24.0, Boy=20.0}}

如您所见，您可以处理Integer和Double列。甚至String可以处理（将选择按字典顺序排列的最大值）。

对于平均，您可以假设您的列值是数字（Number类，Integer或者Double）并收集到Double（整数的平均值也可以是非整数）：

public void AverageTable(int colIdx, int valueIdx, int... rowIdx) {
    Map<Object, Map<Object, Double>> myList = newRows.stream().collect(
            Collectors.groupingBy(r -> r.get(colIdx), Collectors
                    .groupingBy(r -> new PivotColumns(r, rowIdx),
                            Collectors.averagingDouble(r -> ((Number) (r
                                    .get(valueIdx))).doubleValue()))));

    System.out.println("Dynamic AVG PIVOT"); System.out.println(myList);
}

输出：

> p.AverageTable(0, 3, new int[] { 1 });
{West={Girl=12.5, Boy=8.5}, East={Girl=14.0, Boy=12.5}}

> p.AverageTable(0, 4, new int[] { 1 });
{West={Girl=19.0, Boy=16.0}, East={Girl=19.0, Boy=16.0}}