Reversing sorting order of a stream using Comparator.reversed()

Question

I'm writing a program that reads a string as an input and then outputs 10 most repeated words. Problem is, my order is reversed. I want to output from highest to lowest and it's sorted in opposite order. So I've been looking for a solution and only thing I found is .reversed() method but it says "Non-static method cannot be referenced from a static context". I don't understand this error, cause in the example it was used in a similar situation.

I'm new to streams so I'd like to know a simple way to resolve this issue.

public static void main(String[] args) { Scanner scanner = new Scanner(System.in); String input = scanner.nextLine(); List<String> words = Arrays.asList(input.split(" ")); words.stream() .map(word -> word.replaceAll("[^A-Za-z0-9]", "")) .map(String::toLowerCase) .collect(Collectors.groupingBy(Function.identity(), Collectors.counting())) .entrySet() .stream() .sorted(Comparator.comparing(Map.Entry::getValue).reversed()) // static method can't be referenced .limit(10) .sorted(Comparator.comparing(Map.Entry::getKey)) .forEach(e -> System.out.println(e.getKey())); }

EDIT: I've had keys and values of a map mixed up and edited that. Due to my mistake, Arvind's answer might look a bit different, but it doesn't matter since Map.Entry has both .comparingByKey and .comparingByValue methods.

In addition to the below answer, you can also use sorted((Comparator.<Map.Entry<String, Long>, Long>comparing(Map.Entry::getValue)).reversed()) or better: sorted((Map.Entry.<String, Long>comparingByValue()).reversed()) — Aniket Sahrawat
– Aniket Sahrawat, Commented Mar 21, 2021 at 16:47

Arvind Kumar Avinash · Accepted Answer · 2021-03-21 13:16:13Z

`Map.Entry.comparingByKey`

You can pass Comparator.reverseOrder() to Map.Entry.comparingByKey.

import java.util.Arrays; import java.util.Comparator; import java.util.List; import java.util.Map; import java.util.Scanner; import java.util.function.Function; import java.util.stream.Collectors; class Main { public static void main(String[] args) { Scanner scanner = new Scanner(System.in); String input = scanner.nextLine(); List<String> words = Arrays.asList(input.split(" ")); words.stream() .map(word -> word.replaceAll("[^A-Za-z0-9]", "")) .map(String::toLowerCase) .collect(Collectors.groupingBy(Function.identity(), Collectors.counting())) .entrySet() .stream() .sorted(Map.Entry.comparingByKey(Comparator.reverseOrder())) .limit(10) .sorted(Comparator.comparing(Map.Entry::getValue)) .forEach(e -> System.out.println(e.getKey())); } }

A sample run:

1 2 3 4 5 6 7 8 9 1 2 5 9 2 7 2 3 9 5 3 1 8 3 6 8 2 3 6 9 4 7 8 6 5 1 9 3 2

It’s worth noting why it works and the question’s code doesn’t. Type inference has limitations when it comes to chained method invocations whereas it works without problems for nested invocations.

Collectives™ on Stack Overflow

Reversing sorting order of a stream using Comparator.reversed()

1 Answer 1

`Map.Entry.comparingByKey`

1 Comment

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

1 Comment

Related