Streams are convenient way to reduce the line of codes, but an understanding them is equally challenging. I write this blog, after realising a desperate attempt at solving a trivial problem just took overwhelming time. (Could be that I am getting old, but never late to learn things again)
public class PlaySteams {
public static void main(String []args) {
int[] a = new int[] {1,1,1,2,2,2,3,3,3,4,4,4};
//Stream Sum of the array
long sum = IntStream.range(0, a.length).count();
System.out.printf("Sum: %d\n", sum);
// Maximum
System.out.printf("Max: %d\n", IntStream.range(0, a.length).map(i -> Integer.valueOf(a[i])).distinct().max().getAsInt());
// Minimum
System.out.printf("Min: %d\n", IntStream.range(0, a.length).map(i -> Integer.valueOf(a[i])).distinct().min().getAsInt());
IntStream.range(0, a.length).map(i -> Integer.valueOf(a[i])).distinct().forEach(x -> System.out.printf("%d ", x));
System.out.printf("Average (Distinct): %f\n", IntStream.range(0, a.length).map(i -> Integer.valueOf(a[i])).distinct().average().getAsDouble());
System.out.printf(" Number of elements : %d\n", IntStream.of(a).asLongStream().count());
IntStream.range(0, a.length).map(i -> Integer.valueOf(a[i])).forEach(x -> System.out.printf("%d ", x));
System.out.printf("Average (All): %f\n", IntStream.range(0, a.length).map(i -> Integer.valueOf(a[i])).average().getAsDouble());
List<Integer> listOfIntegers = IntStream.of(a).boxed().collect(Collectors.toList());
System.out.println(listOfIntegers.toString());
System.out.println("Length: ");
System.out.println(listOfIntegers.size());
// Creating a map
// 1 -> 3
// 2 -> 3 ...
System.out.println(IntStream.range(0, a.length).map(i -> a[i]).boxed().collect(Collectors.groupingBy(Function.identity(), Collectors.counting())).toString());
// Using list
Map<Integer, Long> valueMap = listOfIntegers.stream().collect(Collectors.groupingBy(Function.identity(), Collectors.counting()));
System.out.println(valueMap.toString());
// Map of indexes
// Indexes and value of the index
System.out.println(IntStream.range(0, a.length).boxed().collect(Collectors.groupingBy( i -> a[Integer.valueOf(i)], Collectors.toList())));
}
}The example set remains the same for all the invocation.
int[] a = new int[] {1,1,1,2,2,2,3,3,3,4,4,4};Example - 1:#
long sum = IntStream.range(0, a.length).count();
System.out.printf("Sum: %d\n", sum);It simply runs over the length of the array and returns the total number of elements
Sum: 12Example - 2:#
Return the maximum
System.out.printf("Max: %d\n", IntStream.range(0, a.length).map(i -> Integer.valueOf(a[i])).distinct().max().getAsInt());Max: 4Example - 3:#
Returns the minimum
System.out.printf("Min: %d\n", IntStream.range(0, a.length).map(i -> Integer.valueOf(a[i])).distinct().min().getAsInt());Min: 1Example - 4:#
Run through the list and print distinct items
IntStream.range(0, a.length).map(i -> Integer.valueOf(a[i])).distinct().forEach(
x ->
System.out.printf("%d ", x));1 2 3 4Example - 5:#
Average of the distinct items
System.out.printf("Average (Distinct): %f\n", IntStream.range(0, a.length).map(i -> Integer.valueOf(a[i])).distinct().average().getAsDouble());Average (Distinct): 2.500000Example - 6:#
Different way of getting the count of elements.
System.out.printf(" Number of elements : %d\n", IntStream.of(a).asLongStream().count());Number of elements : 12Example - 7:#
IntStream.range(0, a.length).map(i -> Integer.valueOf(a[i])).forEach(x -> System.out.printf("%d ", x));Get the list of elements
1 1 1 2 2 2 3 3 3 4 4 4Example - 8:#
System.out.printf("Average (All): %f\n", IntStream.range(0, a.length).map(i -> Integer.valueOf(a[i])).average().getAsDouble());Average (All): 2.500000Example - 9:#
List<Integer> listOfIntegers = IntStream.of(a).boxed().collect(Collectors.toList());
System.out.println(listOfIntegers.toString());[1, 1, 1, 2, 2, 2, 3, 3, 3, 4, 4, 4]Example - 10:#
System.out.println(IntStream.range(0, a.length).map(i -> a[i]).boxed().collect(Collectors.groupingBy(Function.identity(), Collectors.counting())).toString());Creates a map of the value and the number of times it repeats
1=3, 2=3, 3=3, 4=3}Example - 11:#
Map<Integer, Long> valueMap = listOfIntegers.stream().collect(Collectors.groupingBy(Function.identity(), Collectors.counting()));
System.out.println(valueMap.toString());Using list that we had in Example - 9 to get the map.
{1=3, 2=3, 3=3, 4=3}Example - 12:#
Returns the list of index for each value
System.out.println(IntStream.range(0, a.length).boxed().collect(Collectors.groupingBy( i -> a[Integer.valueOf(i)], Collectors.toList())));{1=[0, 1, 2], 2=[3, 4, 5], 3=[6, 7, 8], 4=[9, 10, 11]}