如何转置 List<List>?

问题描述

我有以下 ArrayList，

I have a following ArrayList,

[Title,Data1,Data2,Data3]
[A,2,3,4]
[B,3,5,7]

我想像这样转换这个，

[Title,A,B]
[Data1,2,3]
[Data2,3,5]
[Data3,4,7]

我对这种方法有点困惑.任何提示将不胜感激.

I'm bit confused with the approach. Any hint would be much appreciated.

谢谢.

推荐答案

这叫做换位.以下代码段满足您的需求:

This is called transposition. The following snippet does what you need:

import java.util.*;
public class ListTranspose {
    public static void main(String[] args) {
        Object[][] data = {
            { "Title", "Data1", "Data2", "Data3" },
            { "A", 2, 3, 4 },
            { "B", 3, 5, 7 },
        };
        List<List<Object>> table = new ArrayList<List<Object>>();
        for (Object[] row : data) {
            table.add(Arrays.asList(row));
        }
        System.out.println(table); //  [[Title, Data1, Data2, Data3],
                                   //   [A, 2, 3, 4],
                                   //   [B, 3, 5, 7]]"
        table = transpose(table);
        System.out.println(table); //  [[Title, A, B],
                                   //   [Data1, 2, 3],
                                   //   [Data2, 3, 5],
                                   //   [Data3, 4, 7]]
    }
    static <T> List<List<T>> transpose(List<List<T>> table) {
        List<List<T>> ret = new ArrayList<List<T>>();
        final int N = table.get(0).size();
        for (int i = 0; i < N; i++) {
            List<T> col = new ArrayList<T>();
            for (List<T> row : table) {
                col.add(row.get(i));
            }
            ret.add(col);
        }
        return ret;
    }
}

另见

• 维基百科/转置

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