Remove duplicates from ArrayList from array list

Question

I have a problem, I'm sure the solution is so simple, but I can not find it. I have ArrayListsmaller ArrayLists. These lists contain type elements String. I want to merge smaller lists into one and then remove duplicates. Let me be clear.

I have it:

[[USA, Maine], [USA, Maine, Kennebunk], [USA, Maine, North Berwick], 
[USA, New Hampshire], [USA, Keene, New Hampshire], [USA, Keene, New 
Hampshire, Main Street], [USA, New Hampshire, Swanzey]].

This is my main list with smaller lists inside. I want to have the final one ArrayList, which is a merger of smaller ones and removes duplicates.

I want:

[USA, Maine, Kennebunk, North Berwick, New Hampshire , Keene, Main Street, Swanzey]

Any help is appreciated. thank you

Answer 1

This is a short solution using the class Stream:

listOfLists.stream().flatMap(List::stream).collect(Collectors.toSet())

, Set. .

List, :

listOfLists.stream()
           .flatMap(List::stream)
           .distinct()
           .collect(Collectors.toList())

, , .. [["foo","bar"],["bar","abc","foo"]] ["foo","bar","abc"] . , Set, , .

Answer 2

Sets (Set )

public List<String> merge(List<List<String>> list) {
    Set<String> uniques = new HashSet<>();
    for(List<String> sublist : list) {
        uniques.addAll(sublist);
    }
    return new ArrayList<>(uniques);
}

p.s. , , HashSet TreeSet : Set<String> uniques = new TreeSet<>();

Answer 3

:

Set<String> result = new LinkedHashSet<>();
for (List<String> innerList : filmingLocations) result.addAll(innerList);

result LinkedHashSet, , , .

Java 8:

Set<String> result = new LinkedHashSet<>();
filmingLocations.forEach(result::addAll);

Java 8:

Set<String> result = filmingLocations.stream()
    .flatMap(List::stream)
    .collect(Collectors.toCollection(LinkedHashSet::new));

Answer 4

< Java 8, ArrayList, "resultList". ArrayLists Strings, contains() false. , ArrayList . HashSet, . , ArrayList Collection:

ArrayList<ArrayList<String>> sourceList = new ArrayList<>();
        // Adding sample ArrayLists ("a" and "b") of Strings to sourceList:
        ArrayList<String> a = new ArrayList<>();
        a.add("USA");
        a.add("Maine");
        sourceList.add(a);
        ArrayList<String> b = new ArrayList<>();
        b.add("USA");
        b.add("Maine");
        b.add("Kennebunk");
        sourceList.add(b);
        ArrayList<String> resultList = new ArrayList<>();
        for(ArrayList<String> outerList : sourceList) {
            for(String str : outerList) {
                // If resultList doesn't contain currently checked string...
                if(!(resultList.contains(str))) {
                    // Add this string to resultList...
                    resultList.add(str);
                }
            }
        }
        System.out.println(resultList.toString());

: [USA, Maine, Kennebunk]

Answer 5

:
Loop trough ever String ArrayList ArrayLists ArrayList, , .contains() ArrayList

:

  public ArrayList<String> merge(ArrayList<ArrayList<String>> startArrayList) {
    ArrayList<String> finalArrayList = new ArrayList<String>();
    //Iterate over each element
    for (ArrayList<String> innerList:startArrayList) {
      for (String value:innerList) {
        //add the String if it is missing
        if (!finalArrayList.contains(value))
          finalArrayList.add(value);
      }
    }
    return finalArrayList;
  }

Answer 6

, / - , LOL. ?

- , . O (log n).

public List<String> mergeTowns (List<List<String>> list) {
    Set<String> uniques = new HashSet<>();
    for(List<String> sublist : list) {
        uniques.addAll(sublist);
    }
    return new ArrayList<>(uniques);
}

---

, , , - . , , , , , . , .

. . ​​

[ = [, , , ], = [, , , ], = [, , , ]]

/.

public class Merge {


    private static ArrayList<String> mergeMap(HashMap<String, Set> map) {
        ArrayList<String> data = new ArrayList();
        for(Entry<String, Set> entries : map.entrySet()){
            String country = entries.getKey();
            Set<String> towns = entries.getValue();
            data.add(country+" = "+towns);
        }
        return data;
    }



    public static void main(String[] args) {
        //Mock data
        String[] countrys = {"USA", "CANADA", "MEXICO"};

        //Try this way of building your data structure instead of an array list of array list. 
        HashMap<String,Set> map = new HashMap<String,Set>();
        TreeSet<String> towns = new TreeSet<String>();

        // Add a couple towns to your set of towns
        towns.add("berwick");
        towns.add("north berwick");
        towns.add("kennebunk");
        towns.add("kennebunk");
        towns.add("kennebunk");
        towns.add("kennebunk");
        towns.add("wells");
        towns.add("wells");

        //With a map you could push a different set of towns to different countries
        for(String country: countrys){
            map.put(country, towns);
        }

        //Pass in your map<Country, Towns>
        ArrayList<String> mergedValues = mergeMap(map);
    }
}