Java：通过匹配LinkedHashMap中的相似键来复制值

Question

我有一个LinkedHashMap，想做以下事情：

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HashMap<String, String> nameNum = new LinkedHashMap<String, String>();
nameNum.put("row 1", "data 1");
nameNum.put("Group_Colour_R", "Red");
nameNum.put("Group_Colour_B", "Blue");
nameNum.put("row 4", "data 4");
nameNum.put("row 5", "data 5");
nameNum.put("Group_Shape_R", "Rectangle");
nameNum.put("Group_Shape_T", "Triangle");
nameNum.put("Group_Shape_C", "Circle");
nameNum.put("row 9", "data 9");
nameNum.put("row 10", "data 10");
nameNum.put("row 11", "data 11");

String[] colour = {"Red", "Blue"}; 
String[] shape = {"Rectangle", "Triangle", "Circle"};

import java.util.Map;
import java.util.SortedMap;
import java.util.TreeMap;

import org.apache.commons.lang3.StringUtils;

public class MainClass {
    public static void main(String[] args) {
        SortedMap<String, String> nameNum = new TreeMap<String, String>();
        nameNum.put("row 1", "data 1");
        nameNum.put("Group_Colour_R", "Red");
        nameNum.put("Group_Colour_B", "Blue");
        nameNum.put("row 4", "data 4");
        nameNum.put("row 5", "data 5");
        nameNum.put("Group_Shape_R", "Rectangle");
        nameNum.put("Group_Shape_T", "Triangle");
        nameNum.put("Group_Shape_C", "Circle");
        nameNum.put("row 9", "data 9");
        nameNum.put("row 10", "data 10");
        nameNum.put("row 11", "data 11");


        for (Map.Entry<String, String> entry : nameNum.entrySet()) {
            String prefix = entry.getKey();
            if (prefix.contains("Group")) {
                prefix = prefix.substring(0, StringUtils.lastIndexOf(prefix, "_"));
                System.out.println("******");
                for (Map.Entry<String, String> entry1 : filterPrefix(nameNum, prefix).entrySet()) {
                    System.out.println(entry1);
                }
                System.out.println("******");
            }
        }
    }

    public static <V> SortedMap<String, V> filterPrefix(SortedMap<String,V> baseMap, String prefix) {
        if(prefix.length() > 0) {
            char nextLetter = (char) (prefix.charAt(prefix.length() -1) + 1);
            String end = prefix.substring(0, prefix.length()-1) + nextLetter;
            return baseMap.subMap(prefix, end);
        }
        return baseMap;
    }
}

理想情况下，我希望使用LinkedHashMap，因为我希望保留顺序。我非常感谢关于如何实现类似内容的任何指针/代码。任何代码片段都将受到高度赞赏。提前谢了。

Answer 1

也许Java8StreamAPI在这里会有所帮助。您可以尝试使用collectors.groupingby，将相关条目分组在一起：

Map<String,List<String>> groups =
    nameNum.entrySet()
           .stream()
           .filter(entry -> entry.getKey().contains("Group"))
           .collect(Collectors.groupingBy(entry -> entry.getKey().substring(0, entry.getKey().lastIndexOf("_")),
                                          Collectors.mapping(Map.Entry::getValue,
                                                             Collectors.toList()));

这将生成一个映射包含：

{Group_Shape=[Rectangle, Triangle, Circle], Group_Colour=[Red, Blue]}

如果愿意，还可以强制输出map为LinkedHashmap:

Map<String,List<String>> groups =
    nameNum.entrySet()
           .stream()
           .filter(entry -> entry.getKey().contains("Group"))
           .collect(Collectors.groupingBy(entry -> entry.getKey().substring(0, entry.getKey().lastIndexOf("_")),                     
                                          LinkedHashMap::new, 
                                          Collectors.mapping(Map.Entry::getValue,
                                                             Collectors.toList()));

这将改变输出映射的迭代顺序：

{Group_Colour=[Red, Blue], Group_Shape=[Rectangle, Triangle, Circle]}