iterating and filtering two lists using java 8

Question

I want to iterate two lists and get new filtered list which will have values not present in second list  Can anyone help   I have two lists - one is list of strings  and the other is list of MyClass objects   List lt String gt  list1  List lt MyClass gt  list2   MyClass        MyClass String val                this str   val              String str                        I want filtered list of strings based on -  check second list for elements  abc  whose values not present in list1   List lt String gt  list1   Arrays asList  abc    xyz    lmn     List lt MyClass gt  list2   new ArrayList lt MyClass gt      MyClass obj   new MyClass  abc    list2 add obj   obj   new MyClass  xyz    list2 add obj     Now I want new filtered list -  which will have value     lmn   i e  values not present in list2 whose elements are in list1

User · Answer

Doing it with streams is easy and readable   Predicate lt String gt  notIn2   s - gt    list2 stream   anyMatch mc - gt  s equals mc str    List lt String gt  list3   list1 stream   filter notIn2  collect Collectors toList

User · Answer

If you stream the first list and use a filter based on contains within the second     list1 stream        filter item - gt   list2 contains item     The next question is what code you ll add to the end of this streaming operation to further process the results     over to you   Also  list contains is quite slow  so you would be better with sets   But then if you re using sets  you might find some easier operations to handle this  like removeAll  Set list1        Set list2        Set target   new Set    target addAll list1   target removeAll list2     Given we don t know how you re going to use this  it s not really possible to advise which approach to take

User · Answer

See below  would welcome anyones feedback on the below code    not common between two arrays   List lt String gt  l3  list1 stream   filter x - gt   list2 contains x   collect Collectors toList       Common between two arrays   List lt String gt  l3  list1 stream   filter x - gt  list2 contains x   collect Collectors toList

User · Answer

produce the filter set by streaming the items from list 2    assume list2 has elements of type MyClass where getStr gets the    string that might appear in list1 Set lt String gt  unavailableItems   list2 stream        map MyClass  getStr       collect Collectors toSet         stream the list and use the set to filter it List lt String gt  unavailable   list1 stream                filter e - gt  unavailableItems contains e                collect Collectors toList

User · Answer

if you have class with id and you want to filter by id   line1   you mape all the id  line2  filter what is not exist in the map   Set lt String gt  mapId   entityResponse getEntities   stream   map Entity  getId  collect Collectors toSet      List lt String gt  entityNotExist   entityValues stream   filter n - gt   mapId contains n getId     map DTOEntity  getId  collect Collectors toList

User · Answer

List lt String gt  unavailable   list1 stream                    filter e - gt   list2 stream                            filter d - gt  d getStr   equals e                            count    lt 1                           collect Collectors toList      for this if i change to   List lt String gt  unavailable   list1 stream                    filter e - gt   list2 stream                            filter d - gt  d getStr   equals e                            count    gt 0                           collect Collectors toList      will it give me list1 matched with list2 right

User · Answer

list1   list1 stream   filter str1- gt           list2 stream   map x- gt x getStr    collect Collectors toSet             contains str1   collect Collectors toList       This may work more efficient

User · Answer

DSchmdit answer worked for me  I would like to add on that  So my requirement was to filter a file based on some configurations stored in the table  The file is first retrieved and collected as list of dtos  I receive the configurations from the db and store it as another list  This is how I made the filtering work with streams      List lt FPRSDeferralModel gt  modelList   Files              lines Paths get  src main resources rootFiles XXXXX txt    parallel   parallel                map line - gt                    FileModel fileModel  new FileModel                    line   line trim                    if  line    null  amp  amp   line isEmpty                          System out println  line    line                       fileModel setPlanId Long parseLong line substring 0  5                         fileModel setDivisionList line substring 15  30                        fileModel setRegionList line substring 31  50                        Map lt String  String gt  newMap   new HashedMap lt  gt                         newMap put  other   line substring 51  80                        fileModel setOtherDetailsMap newMap                                      return fileModel                 collect Collectors toList          for  FileModel model   modelList            System out println  model     model              DbConfigModelList respList   populate        System out println  after populate        List lt DbConfig gt  respModelList   respList getFeedbackResponseList          Predicate lt FileModel gt  somePre   s - gt  respModelList stream   anyMatch respitem - gt             System out println  sinde respitem   respitem getPrimaryConfig   getPlanId             System out println  s getPlanid    s getPlanId             System out println  s getPlanId      respitem getPrimaryConfig   getPlanId               s getPlanId   compareTo respitem getPrimaryConfig   getPlanId               return s getPlanId   compareTo respitem getPrimaryConfig   getPlanId       0                  amp  amp   s getSsnId      null               final List lt FileModel gt  finalList    modelList stream   parallel   filter somePre  collect Collectors toList       finalList stream   forEach item - gt         System out println  filtered item is   item          The details are in the implementation of filter predicates  This proves much more perfomant over iterating over loops and filtering out

User · Answer

this can be achieved using below     List lt String gt  unavailable   list1 stream                                filter e - gt   list2 contains e                                collect Collectors toList

[java] iterating and filtering two lists using java 8

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