Ho to Filter List By Comparing between two lists and if an id exist on second list then take the val-CodePudding

I have two list appIndustries and tenantAppIndustries both having List of values :

    List<String> industries = new ArrayList<>();
    List<AppIndustryDto> appIndustries ;
    List<AppIndustryDto> tenantAppIndustries ;

    public class AppIndustryDto {
    public String appId;
    public String industryId;
   }

     Both List having data
  Inside appIndustries list I am getting ->
  a1 i1
  a1 i2
  a2 i3
  a3 i1
 Inside tenantAppIndustries list I am getting ->
 a1 i4

Final Response should be industries list should have [i1,i3,i4]

Please help me I am a beginner, thanks for you reply.

CodePudding user response：

Try this.

public static void main(String[] args) {
    List<AppIndustryDto> appIndustries = List.of(
        new AppIndustryDto("a1", "i1"),
        new AppIndustryDto("a1", "i2"),
        new AppIndustryDto("a2", "i3"),
        new AppIndustryDto("a3", "i1"));

    List<AppIndustryDto> tenantAppIndustries = List.of(
        new AppIndustryDto("a1", "i4"));

    Map<String, String> tenantMap = tenantAppIndustries.stream()
        .collect(Collectors.toMap(a -> a.appId, a -> a.industryId, (a, b) -> a));
        // If the appId is duplicated, select the first one.

    List<String> industries = appIndustries.stream()
        .map(a -> tenantMap.getOrDefault(a.appId, a.industryId))
        .distinct()
        .toList();

    System.out.println(industries);
}

output:

[i4, i3, i1]

CodePudding user response：

You can try this

List<String> list = appIndustries.stream()
.map(app -> {
  AppIndustryDto dto = tenantAppIndustries.stream()
                              .filter(t -> t.appId.equals(app.appId))
                              .findAny()
                              .orElse(null);
  return dto==null ? app.industryId : dto.industryId ;
})
.distinct()
.collect(Collectors.toList());