Separate Odd and Even numbers (List<Integer> to Map<String, List<Integer>>)
Map<String, List<Integer>> oddEvenMap = numbers.stream()
.collect(Collectors.groupingBy(i -> (i % 2 != 0 ? "Odd" : "Even")));
Find distinct values from Map<String, List<Integer>
Set<Integer> set = map.values().stream()
.flatMap(Collection::stream)
.collect(Collectors.toSet());
Biggest Odd and Even from List (List<Integer> to Map<String, Integer>)
Map<String, Integer> bigOddEven = numbers.stream().collect(Collectors.toMap(i -> (i % 2 == 0 ? "Even" : "Odd"), Function.identity(), (i1 , i2) -> i1 > i2 ? i1 : i2));
Use value as key and create new map from existing
Map<String, Integer> map = new HashMap<>();
map.put("a", 1);
map.put("b", 1);
map.put("c", 2);
Map<Integer, List<String>> ans = map.keySet().stream().collect(Collectors.groupingBy(map::get));
System.out.println(ans);
Output
{1=[a, b], 2=[c]}
Find frequency of each number in list
List<Integer> numbers = new ArrayList<>();
numbers.add(1);
numbers.add(2);
numbers.add(3);
numbers.add(4);
numbers.add(4);
Map<Integer, Long> ans = numbers.stream()
.collect(Collectors.groupingBy(Function.identity(), Collectors.counting()));
System.out.println(ans);
Output
{1=1, 2=1, 3=1, 4=2}
Remove from map based on condition on values
Map<String, Integer> map = new HashMap<>();
map.put("a", 1);
map.put("b", 1);
map.put("c", 2);
map.values().removeIf(i -> i == 1);
System.out.println(map);
Output
{c=2}
Distinct and Sum of numbers
Stream<Integer> distinct = numbers.stream().distinct();
int s = numbers.stream().mapToInt(Integer::intValue).sum();
IntSummaryStatistics for Average, Sum, Min/Max
IntSummaryStatistics intSummaryStatistics = numbers.stream().mapToInt(Integer::intValue).summaryStatistics();
double average = intSummaryStatistics.getAverage();
long sum = intSummaryStatistics.getSum();
int max = intSummaryStatistics.getMax();
int min = intSummaryStatistics.getMin();
long count = intSummaryStatistics.getCount();
