How to remove an element of a HashMap whilst streaming (lambda)

Question

I have the following situation where I need to remove an element from a stream.

map.entrySet().stream().filter(t -> t.getValue().equals(\"0\")).
                 


        

Answer 1

1st time replying. Ran across this thread and thought to update if others are searching. Using streams you can return a filtered map<> or whatever you like really.

  @Test
  public void test() {

    Map<String,String> map1 = new HashMap<>();
    map1.put("dan", "good");
    map1.put("Jess", "Good");
    map1.put("Jaxon", "Bad");
    map1.put("Maggie", "Great");
    map1.put("Allie", "Bad");

    System.out.println("\nFilter on key ...");
    Map<String,String> map2 = map1.entrySet().stream().filter(x -> 
    x.getKey().startsWith("J"))
        .collect(Collectors.toMap(e -> e.getKey(), e -> e.getValue()));

    map2.entrySet()
      .forEach(s -> System.out.println(s));

    System.out.println("\nFilter on value ...");
    map1.entrySet().stream()
      .filter(x -> !x.getValue().equalsIgnoreCase("bad"))
      .collect(Collectors.toMap(e -> e.getKey(),  e -> e.getValue()))
      .entrySet().stream()
      .forEach(s -> System.out.println(s));
  }

------- output -------

Filter on key ...
Jaxon=Bad
Jess=Good

Filter on value ...
dan=good
Jess=Good
Maggie=Great

Answer 2

map.entrySet().removeIf(entry -> entry.getValue().equals("0"));

You can't do it with streams, but you can do it with the other new methods.

EDIT: even better:

map.values().removeAll(Collections.singleton("0"));

Answer 3

I think it's not possible (or deffinitelly shouldn't be done) due to Streams' desire to have Non-iterference, as described here

If you think about streams as your functional programming constructs leaked into Java, then think about the objects that support them as their Functional counterparts and in functional programming you operate on immutable objects

And for the best way to deal with this is to use filter just like you did

Answer 4

If you want to remove the entire key, then use:

myMap.entrySet().removeIf(map -> map.getValue().containsValue("0"));