Question

必须将HashMap列表分组为基于密钥具有相同时间戳的HashMap列表。

    Map<String, Object> m0 = new HashMap<>();
        m0.put("x", "aaa#0322");
        m0.put("y", "saadaad");
        m0.put("z", "7asasada89");

        Map<String, Object> m1 = new HashMap<>();
        m1.put("x", "bbb#0314");
        m1.put("y", "asasadafa");
        m1.put("z", "daasaada");

        Map<String, Object> m2 = new HashMap<>();
        m2.put("x", "bbb#0322");
        m2.put("y", "asasdfaff");
        m2.put("z", "2sadada22");
        List<Map> l = new ArrayList<>(Arrays.asList(m0, m1, m2));

[{{x = aaa＃0322，y = saadaad，z = 7asasada89}，{x = bbb＃0314，y = asasadafa，z = daasaada}，{x = bbb＃0322，y = asasdfaff，z = 2sadada22 }，{x = bbb＃0314，y = bsaadda，z = asfasaafe}]

Convert to a format where i can group it according to timestamp value in x like x#0322
         [
            [
                {x=aaa#0322, y=saadaad, z=7asasada89}, {x=bbb#0322, y=asasdfaff, z=2sadada22}
            ], 
            [
                {x=bbb#0314, y=asasadafa, z=daasaada}, {x=bbb#0314, y=bsaadda, z=asfasaafe}
            ]
        ]

Or Convert to a format where i can group it according to timestamp value in x like x#0322 
         [
            {
                {x=aaa#0322, y=saadaad, z=7asasada89}, {x=bbb#0322, y=asasdfaff, z=2sadada22}
            }, 
            {
                {x=bbb#0314, y=asasadafa, z=daasaada}, {x=bbb#0314, y=bsaadda, z=asfasaafe}
            }
        ]

Answer 1

基本上，如果Map包含键x，则根据值进行分组

  List<List<Map<String, String>>> result =  l.stream()
      .filter(m->m.containsKey("x"))    // filter map with `x` key
      .collect(Collectors.groupingBy(m->m.get("x").split("#")[1]))   // if map contains `x` as key then group by the value after `#`
      .entrySet().stream()
      .sorted(Map.Entry.comparingByKey(Comparator.reverseOrder()))    //sort on requirement
      .map(Entry::getValue)
      .collect(Collectors.toList());

输出

[[{x=bbb#123, y=asasdfaff, z=2sadada22}], [{x=aaa#123, y=saadaad, z=7asasada89}], [{x=bbb#000, y=asasadafa, z=daasaada}]]

根据关键的Java流将HashMap列表分组为HashMap列表

1 个答案: