user1639485 :
I have a Map<String, List<String>>. I want to transform this map to a List after filtering on the map's key.
Example:
Map<String, List<String>> words = new HashMap<>();
List<String> aList = new ArrayList<>();
aList.add("Apple");
aList.add("Abacus");
List<String> bList = new ArrayList<>();
bList.add("Bus");
bList.add("Blue");
words.put("A", aList);
words.put("B", bList);
Given a key, say, "B"
Expected Output: ["Bus", "Blue"]
This is what I am trying:
List<String> wordsForGivenAlphabet = words.entrySet().stream()
.filter(x-> x.getKey().equalsIgnoreCase(inputAlphabet))
.map(x->x.getValue())
.collect(Collectors.toList());
I am getting an error. Can someone provide me with a way to do it in Java8?
Beri :
Your sniplet wil produce a List<List<String>> not List<String>.
You are missing flatMap , that will convert stream of lists into a single stream, so basically flattens your stream:
List<String> wordsForGivenAlphabet = words.entrySet().stream()
.filter(x-> x.getKey().equalsIgnoreCase(inputAlphabet))
.map(Map.Entry::getValue)
.flatMap(List::stream)
.collect(Collectors.toList());
You can also add distinct(), if you don't want values to repeat.
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