I got a group of Integers and I want to count the amount of max() integers my stream contains. The max() method is from within the Stream API.
I was going for something like this
int count = Arrays.stream(myIntArray)
.filter(i -> i == max())
.count();
System.out.printf("Count: %d", count);
I can't call the max() method from within my forEach() method since that's not how Streams function – so what can I do to make this work?
You can't do anything like this, not without a lot of hassle. The simplest way of writing what you want would be two stages:
int max = Arrays.stream(array).max().getAsInt();
int count = (int) Arrays.stream(array).filter(i -> i == max).count();
If you insist on doing it in one pass, I'd write something like
int[] maxAndCount = Arrays.stream(array).collect(
() -> new int[2], // first max, then count
(maxAndCount, i) -> {
if (i > maxAndCount[0] || maxAndCount[1] == 0) {
maxAndCount[0] = i;
maxAndCount[1] = 1;
} else if (i == maxAndCount[0]) {
maxAndCount[1]++;
}
},
(maxAndCount1, maxAndCount2) -> {
if (maxAndCount1[0] < maxAndCount2[0]) {
maxAndCount1[0] = maxAndCount2[0];
maxAndCount1[1] = maxAndCount2[1];
} else if (maxAndCount1[0] == maxAndCount2[0]) {
maxAndCount1[1] += maxAndCount2[1];
}
});
int count = maxAndCount[1];
...but honestly, the simple two-stage version is hard to beat. (And frankly I'd expect it to perform better.)
Arrays.stream(int[])
getAsInt() means that an empty array will fail with NoSuchElementException, rather than result in a max count of 0 (there are no max elements, so the count of them is 0). Since OP is only interested in the count, not the max value itself, using orElse(0) would be better.filter() predicate or the collect() accumulator is about the same thing, but the double-streaming means that you have the overhead of sending the iterated values down-stream twice, which is using the heap. --- Anyway, kinda moot point, because if you truly wanted fast, you wouldn't be using stream for this, just a regular for loop, so I agree that the two-liner is better / simpler / easier to understand, but performance is not why.orElse(0).If you want to use streams for this, you have to use an object that holds the state - you could use a custom collector for this task:
public static void main(String[] args) {
final int[] arr = {1, 2, 3, 4, 5, 1, 2, 3, 5};
class MaxCollector {
int max = Integer.MIN_VALUE;
int count = 0;
public void accept(int value) {
if (max < value) {
max = value;
count = 1;
} else if (max == value) {
count++;
}
}
public void combine(MaxCollector other) {
if (max == other.max) {
count += other.count;
} else if (max < other.max) {
max = other.max;
count = other.count;
}
}
}
final MaxCollector m = Arrays.stream(arr).collect(
MaxCollector::new, MaxCollector::accept, MaxCollector::combine);
System.out.println(m.max + " : " + m.count);
}
You can use the below streams code (with inline comments) as well which gives the number of occurrences (of the maximum number):
int maxValueCount = Arrays.stream(myIntArray).
collect(Collectors.groupingBy(Function.identity(),
Collectors.counting())).//group by numbers and counts first
entrySet().stream().//get Elements from group Map
max((entry1, entry2) ->
(int)(entry1.getValue() - entry2.getValue())).//find max number in map
get().getValue();//get the count of maximum number
You could get the max first, then stream it.
int max = Arrays.stream(myIntArray).max().getAsInt();
int count = Arrays.stream(myIntArray)
.filter(i -> i == max)
.count();
System.out.printf("Count: %d", count);
Just use the frequency method in Collections class. It exists exactly for this purpose.
max()return?max()returns the largest Integer in the array Stream.