Group a List of HashMaps to a list of HashMaps based on a key java streams

user1712810 :

Have to group a List of HashMaps to a list of HashMaps that have same timestamps based on a key.

    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}
            }
        ]

Deadpool :

Basically if Map contains key x then do a group by based on value

  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());

output

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