Refactor Java8GroupingByCollectorUnitTest
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package com.baeldung.java8;
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import static java.util.Comparator.comparingInt;
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import static java.util.stream.Collectors.averagingInt;
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import static java.util.stream.Collectors.counting;
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import static java.util.stream.Collectors.groupingBy;
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import static java.util.stream.Collectors.groupingByConcurrent;
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import static java.util.stream.Collectors.joining;
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import static java.util.stream.Collectors.mapping;
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import static java.util.stream.Collectors.maxBy;
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import static java.util.stream.Collectors.summarizingInt;
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import static java.util.stream.Collectors.summingInt;
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import static java.util.stream.Collectors.toList;
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import static java.util.stream.Collectors.toSet;
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import static org.junit.Assert.assertEquals;
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import static org.junit.Assert.assertNull;
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import static org.junit.Assert.assertTrue;
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import java.util.Arrays;
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import java.util.EnumMap;
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import java.util.IntSummaryStatistics;
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import java.util.List;
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import java.util.Map;
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import java.util.Optional;
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import java.util.Set;
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import java.util.concurrent.ConcurrentMap;
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import org.junit.Test;
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import com.baeldung.java_8_features.groupingby.BlogPost;
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import com.baeldung.java_8_features.groupingby.BlogPostType;
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import org.junit.Test;
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import java.util.*;
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import java.util.concurrent.ConcurrentMap;
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import static java.util.Comparator.comparingInt;
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import static java.util.stream.Collectors.*;
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import static org.junit.Assert.*;
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public class Java8GroupingByCollectorUnitTest {
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private static final List<BlogPost> POSTS = Arrays.asList(new BlogPost("News item 1", "Author 1", BlogPostType.NEWS, 15), new BlogPost("Tech review 1", "Author 2", BlogPostType.REVIEW, 5),
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new BlogPost("Programming guide", "Author 1", BlogPostType.GUIDE, 20), new BlogPost("News item 2", "Author 2", BlogPostType.NEWS, 35), new BlogPost("Tech review 2", "Author 1", BlogPostType.REVIEW, 15));
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private static final List<BlogPost> posts = Arrays.asList(
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new BlogPost("News item 1", "Author 1", BlogPostType.NEWS, 15),
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new BlogPost("Tech review 1", "Author 2", BlogPostType.REVIEW, 5),
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new BlogPost("Programming guide", "Author 1", BlogPostType.GUIDE, 20),
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new BlogPost("News item 2", "Author 2", BlogPostType.NEWS, 35),
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new BlogPost("Tech review 2", "Author 1", BlogPostType.REVIEW, 15));
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@Test
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public void givenAListOfPosts_whenGroupedByType_thenGetAMapBetweenTypeAndPosts() {
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Map<BlogPostType, List<BlogPost>> postsPerType = POSTS.stream().collect(groupingBy(BlogPost::getType));
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Map<BlogPostType, List<BlogPost>> postsPerType = posts
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.stream()
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.collect(groupingBy(BlogPost::getType));
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assertEquals(2, postsPerType.get(BlogPostType.NEWS).size());
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assertEquals(1, postsPerType.get(BlogPostType.GUIDE).size());
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assertEquals(2, postsPerType.get(BlogPostType.REVIEW).size());
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assertEquals(2, postsPerType
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.get(BlogPostType.NEWS)
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.size());
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assertEquals(1, postsPerType
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.get(BlogPostType.GUIDE)
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.size());
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assertEquals(2, postsPerType
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.get(BlogPostType.REVIEW)
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.size());
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}
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@Test
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public void givenAListOfPosts_whenGroupedByTypeAndTheirTitlesAreJoinedInAString_thenGetAMapBetweenTypeAndCsvTitles() {
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Map<BlogPostType, String> postsPerType = POSTS.stream().collect(groupingBy(BlogPost::getType, mapping(BlogPost::getTitle, joining(", ", "Post titles: [", "]"))));
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Map<BlogPostType, String> postsPerType = posts
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.stream()
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.collect(groupingBy(BlogPost::getType, mapping(BlogPost::getTitle, joining(", ", "Post titles: [", "]"))));
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assertEquals("Post titles: [News item 1, News item 2]", postsPerType.get(BlogPostType.NEWS));
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assertEquals("Post titles: [Programming guide]", postsPerType.get(BlogPostType.GUIDE));
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@ -55,88 +50,174 @@ public class Java8GroupingByCollectorUnitTest {
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@Test
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public void givenAListOfPosts_whenGroupedByTypeAndSumTheLikes_thenGetAMapBetweenTypeAndPostLikes() {
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Map<BlogPostType, Integer> likesPerType = POSTS.stream().collect(groupingBy(BlogPost::getType, summingInt(BlogPost::getLikes)));
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Map<BlogPostType, Integer> likesPerType = posts
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.stream()
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.collect(groupingBy(BlogPost::getType, summingInt(BlogPost::getLikes)));
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assertEquals(50, likesPerType.get(BlogPostType.NEWS).intValue());
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assertEquals(20, likesPerType.get(BlogPostType.REVIEW).intValue());
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assertEquals(20, likesPerType.get(BlogPostType.GUIDE).intValue());
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assertEquals(50, likesPerType
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.get(BlogPostType.NEWS)
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.intValue());
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assertEquals(20, likesPerType
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.get(BlogPostType.REVIEW)
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.intValue());
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assertEquals(20, likesPerType
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.get(BlogPostType.GUIDE)
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.intValue());
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}
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@Test
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public void givenAListOfPosts_whenGroupedByTypeInAnEnumMap_thenGetAnEnumMapBetweenTypeAndPosts() {
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EnumMap<BlogPostType, List<BlogPost>> postsPerType = POSTS.stream().collect(groupingBy(BlogPost::getType, () -> new EnumMap<>(BlogPostType.class), toList()));
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EnumMap<BlogPostType, List<BlogPost>> postsPerType = posts
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.stream()
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.collect(groupingBy(BlogPost::getType, () -> new EnumMap<>(BlogPostType.class), toList()));
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assertEquals(2, postsPerType.get(BlogPostType.NEWS).size());
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assertEquals(1, postsPerType.get(BlogPostType.GUIDE).size());
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assertEquals(2, postsPerType.get(BlogPostType.REVIEW).size());
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assertEquals(2, postsPerType
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.get(BlogPostType.NEWS)
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.size());
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assertEquals(1, postsPerType
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.get(BlogPostType.GUIDE)
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.size());
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assertEquals(2, postsPerType
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.get(BlogPostType.REVIEW)
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.size());
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}
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@Test
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public void givenAListOfPosts_whenGroupedByTypeInSets_thenGetAMapBetweenTypesAndSetsOfPosts() {
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Map<BlogPostType, Set<BlogPost>> postsPerType = POSTS.stream().collect(groupingBy(BlogPost::getType, toSet()));
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Map<BlogPostType, Set<BlogPost>> postsPerType = posts
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.stream()
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.collect(groupingBy(BlogPost::getType, toSet()));
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assertEquals(2, postsPerType.get(BlogPostType.NEWS).size());
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assertEquals(1, postsPerType.get(BlogPostType.GUIDE).size());
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assertEquals(2, postsPerType.get(BlogPostType.REVIEW).size());
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assertEquals(2, postsPerType
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.get(BlogPostType.NEWS)
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.size());
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assertEquals(1, postsPerType
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.get(BlogPostType.GUIDE)
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.size());
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assertEquals(2, postsPerType
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.get(BlogPostType.REVIEW)
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.size());
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}
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@Test
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public void givenAListOfPosts_whenGroupedByTypeConcurrently_thenGetAMapBetweenTypeAndPosts() {
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ConcurrentMap<BlogPostType, List<BlogPost>> postsPerType = POSTS.parallelStream().collect(groupingByConcurrent(BlogPost::getType));
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ConcurrentMap<BlogPostType, List<BlogPost>> postsPerType = posts
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.parallelStream()
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.collect(groupingByConcurrent(BlogPost::getType));
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assertEquals(2, postsPerType.get(BlogPostType.NEWS).size());
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assertEquals(1, postsPerType.get(BlogPostType.GUIDE).size());
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assertEquals(2, postsPerType.get(BlogPostType.REVIEW).size());
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assertEquals(2, postsPerType
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.get(BlogPostType.NEWS)
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.size());
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assertEquals(1, postsPerType
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.get(BlogPostType.GUIDE)
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.size());
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assertEquals(2, postsPerType
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.get(BlogPostType.REVIEW)
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.size());
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}
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@Test
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public void givenAListOfPosts_whenGroupedByTypeAndAveragingLikes_thenGetAMapBetweenTypeAndAverageNumberOfLikes() {
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Map<BlogPostType, Double> averageLikesPerType = POSTS.stream().collect(groupingBy(BlogPost::getType, averagingInt(BlogPost::getLikes)));
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Map<BlogPostType, Double> averageLikesPerType = posts
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.stream()
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.collect(groupingBy(BlogPost::getType, averagingInt(BlogPost::getLikes)));
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assertEquals(25, averageLikesPerType.get(BlogPostType.NEWS).intValue());
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assertEquals(20, averageLikesPerType.get(BlogPostType.GUIDE).intValue());
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assertEquals(10, averageLikesPerType.get(BlogPostType.REVIEW).intValue());
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assertEquals(25, averageLikesPerType
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.get(BlogPostType.NEWS)
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.intValue());
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assertEquals(20, averageLikesPerType
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.get(BlogPostType.GUIDE)
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.intValue());
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assertEquals(10, averageLikesPerType
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.get(BlogPostType.REVIEW)
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.intValue());
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}
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@Test
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public void givenAListOfPosts_whenGroupedByTypeAndCounted_thenGetAMapBetweenTypeAndNumberOfPosts() {
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Map<BlogPostType, Long> numberOfPostsPerType = POSTS.stream().collect(groupingBy(BlogPost::getType, counting()));
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Map<BlogPostType, Long> numberOfPostsPerType = posts
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.stream()
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.collect(groupingBy(BlogPost::getType, counting()));
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assertEquals(2, numberOfPostsPerType.get(BlogPostType.NEWS).intValue());
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assertEquals(1, numberOfPostsPerType.get(BlogPostType.GUIDE).intValue());
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assertEquals(2, numberOfPostsPerType.get(BlogPostType.REVIEW).intValue());
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assertEquals(2, numberOfPostsPerType
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.get(BlogPostType.NEWS)
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.intValue());
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assertEquals(1, numberOfPostsPerType
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.get(BlogPostType.GUIDE)
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.intValue());
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assertEquals(2, numberOfPostsPerType
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.get(BlogPostType.REVIEW)
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.intValue());
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}
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@Test
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public void givenAListOfPosts_whenGroupedByTypeAndMaxingLikes_thenGetAMapBetweenTypeAndMaximumNumberOfLikes() {
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Map<BlogPostType, Optional<BlogPost>> maxLikesPerPostType = POSTS.stream().collect(groupingBy(BlogPost::getType, maxBy(comparingInt(BlogPost::getLikes))));
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Map<BlogPostType, Optional<BlogPost>> maxLikesPerPostType = posts
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.stream()
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.collect(groupingBy(BlogPost::getType, maxBy(comparingInt(BlogPost::getLikes))));
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assertTrue(maxLikesPerPostType.get(BlogPostType.NEWS).isPresent());
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assertEquals(35, maxLikesPerPostType.get(BlogPostType.NEWS).get().getLikes());
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assertTrue(maxLikesPerPostType
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.get(BlogPostType.NEWS)
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.isPresent());
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assertEquals(35, maxLikesPerPostType
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.get(BlogPostType.NEWS)
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.get()
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.getLikes());
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assertTrue(maxLikesPerPostType.get(BlogPostType.GUIDE).isPresent());
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assertEquals(20, maxLikesPerPostType.get(BlogPostType.GUIDE).get().getLikes());
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assertTrue(maxLikesPerPostType
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.get(BlogPostType.GUIDE)
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.isPresent());
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assertEquals(20, maxLikesPerPostType
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.get(BlogPostType.GUIDE)
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.get()
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.getLikes());
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assertTrue(maxLikesPerPostType.get(BlogPostType.REVIEW).isPresent());
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assertEquals(15, maxLikesPerPostType.get(BlogPostType.REVIEW).get().getLikes());
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assertTrue(maxLikesPerPostType
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.get(BlogPostType.REVIEW)
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.isPresent());
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assertEquals(15, maxLikesPerPostType
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.get(BlogPostType.REVIEW)
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.get()
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.getLikes());
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}
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@Test
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public void givenAListOfPosts_whenGroupedByAuthorAndThenByType_thenGetAMapBetweenAuthorAndMapsBetweenTypeAndBlogPosts() {
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Map<String, Map<BlogPostType, List<BlogPost>>> map = POSTS.stream().collect(groupingBy(BlogPost::getAuthor, groupingBy(BlogPost::getType)));
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Map<String, Map<BlogPostType, List<BlogPost>>> map = posts
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.stream()
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.collect(groupingBy(BlogPost::getAuthor, groupingBy(BlogPost::getType)));
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assertEquals(1, map.get("Author 1").get(BlogPostType.NEWS).size());
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assertEquals(1, map.get("Author 1").get(BlogPostType.GUIDE).size());
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assertEquals(1, map.get("Author 1").get(BlogPostType.REVIEW).size());
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assertEquals(1, map
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.get("Author 1")
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.get(BlogPostType.NEWS)
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.size());
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assertEquals(1, map
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.get("Author 1")
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.get(BlogPostType.GUIDE)
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.size());
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assertEquals(1, map
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.get("Author 1")
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.get(BlogPostType.REVIEW)
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.size());
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assertEquals(1, map.get("Author 2").get(BlogPostType.NEWS).size());
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assertEquals(1, map.get("Author 2").get(BlogPostType.REVIEW).size());
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assertNull(map.get("Author 2").get(BlogPostType.GUIDE));
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assertEquals(1, map
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.get("Author 2")
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.get(BlogPostType.NEWS)
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.size());
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assertEquals(1, map
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.get("Author 2")
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.get(BlogPostType.REVIEW)
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.size());
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assertNull(map
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.get("Author 2")
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.get(BlogPostType.GUIDE));
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}
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@Test
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public void givenAListOfPosts_whenGroupedByTypeAndSummarizingLikes_thenGetAMapBetweenTypeAndSummary() {
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Map<BlogPostType, IntSummaryStatistics> likeStatisticsPerType = POSTS.stream().collect(groupingBy(BlogPost::getType, summarizingInt(BlogPost::getLikes)));
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Map<BlogPostType, IntSummaryStatistics> likeStatisticsPerType = posts
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.stream()
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.collect(groupingBy(BlogPost::getType, summarizingInt(BlogPost::getLikes)));
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IntSummaryStatistics newsLikeStatistics = likeStatisticsPerType.get(BlogPostType.NEWS);
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