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mbarriolambarriola
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Bael 5073 guide to multi map (eugenp#11179)
* Commit source code to branch * BAEL-5065 improvement of groupBy with complex key * Source code for Guide to Stream::mapMulti
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‎core-java-modules/core-java-16/src/main/java/com/baeldung/java_16_features/mapmulti/Album.java‎

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package com.baeldung.java_16_features.mapmulti;
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import java.util.List;
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import java.util.function.Consumer;
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import java.util.stream.Collectors;
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import org.apache.commons.lang3.tuple.ImmutablePair;
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import org.apache.commons.lang3.tuple.Pair;
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public class Album {
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private String albumName;
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private int albumCost;
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private List<Artist> artists;
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Album(String name, int albumCost, List<Artist> artists) {
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this.albumName = name;
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this.artists = artists;
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this.albumCost = albumCost;
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}
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public void artistAlbumPairsToMajorLabels(Consumer<Pair<String, String>> consumer) {
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for (Artist artist : artists) {
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if (artist.isAssociatedMajorLabels()) {
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String concatLabels = artist.getMajorLabels()
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.stream()
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.collect(Collectors.joining(","));
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consumer.accept(new ImmutablePair<>(artist.getName() + ":" + albumName, concatLabels));
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}
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}
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}
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public String getAlbumName() {
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return albumName;
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}
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public int getAlbumCost() {
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return albumCost;
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}
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List<Artist> getArtists() {
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return artists;
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}
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public String toString() {
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return albumName;
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}
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}

‎core-java-modules/core-java-16/src/main/java/com/baeldung/java_16_features/mapmulti/Artist.java‎

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package com.baeldung.java_16_features.mapmulti;
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import java.util.List;
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import java.util.Objects;
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public class Artist {
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private final String name;
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private boolean associatedMajorLabels;
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private List<String> majorLabels;
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Artist(String name, boolean associatedMajorLabels, List<String> majorLabels) {
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this.name = name;
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this.associatedMajorLabels = associatedMajorLabels;
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this.majorLabels = majorLabels;
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}
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public String getName() {
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return name;
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}
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public boolean isAssociatedMajorLabels() {
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return associatedMajorLabels;
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}
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public List<String> getMajorLabels() {
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return majorLabels;
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}
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@Override
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public int hashCode() {
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return Objects.hash(name);
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}
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@Override
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public boolean equals(Object obj) {
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if (this == obj)
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return true;
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if (obj == null)
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return false;
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if (getClass() != obj.getClass())
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return false;
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Artist other = (Artist) obj;
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return Objects.equals(name, other.name);
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}
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public String toString() {
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return name;
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}
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}

‎core-java-modules/core-java-16/src/test/java/com/baeldung/java_16_features/mapmulti/JavaStreamMapMultiUnitTest.java‎

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package com.baeldung.java_16_features.mapmulti;
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import static java.util.stream.Collectors.toList;
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import static org.assertj.core.api.Assertions.assertThat;
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import static org.assertj.core.api.Assertions.offset;
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import static org.junit.jupiter.api.Assertions.assertTrue;
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import java.util.Arrays;
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import java.util.List;
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import org.apache.commons.lang3.tuple.ImmutablePair;
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import org.apache.commons.lang3.tuple.Pair;
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import org.junit.jupiter.api.Test;
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public class JavaStreamMapMultiUnitTest {
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private static final List<Album> albums = Arrays.asList(new Album("album1", 10, Arrays.asList(new Artist("bob", true, Arrays.asList("label1", "label3")), new Artist("tom", true, Arrays.asList("label2", "label3")))),
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new Album("album2", 20, Arrays.asList(new Artist("bill", true, Arrays.asList("label2", "label3")), new Artist("tom", true, Arrays.asList("label2", "label4")))));
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@Test
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public void givenAListOfintegers_whenMapMulti_thenGetListOfOfEvenDoublesPlusPercentage() {
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List<Integer> integers = Arrays.asList(1, 2, 3, 4, 5);
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double percentage = .01;
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List<Double> evenDoubles = integers.stream()
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.<Double> mapMulti((integer, consumer) -> {
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if (integer % 2 == 0) {
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consumer.accept((double) integer * (1 + percentage));
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}
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})
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.collect(toList());
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assertThat(evenDoubles).containsAll(Arrays.asList(2.02D, 4.04D));
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}
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@Test
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public void givenAListOfintegers_whenFilterMap_thenGetListOfOfEvenDoublesPlusPercentage() {
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List<Integer> integers = Arrays.asList(1, 2, 3, 4, 5);
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double percentage = .01;
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List<Double> evenDoubles = integers.stream()
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.filter(integer -> integer % 2 == 0)
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.<Double> map(integer -> ((double) integer * (1 + percentage)))
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.collect(toList());
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assertThat(evenDoubles).containsAll(Arrays.asList(2.02D, 4.04D));
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}
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@Test
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public void givenAListOfintegers_whenMapMultiToDouble_thenGetSumOfEvenNumbersAfterApplyPercentage() {
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List<Integer> integers = Arrays.asList(1, 2, 3, 4, 5, 6, 7);
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double percentage = .01;
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double sum = integers.stream()
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.mapMultiToDouble((integer, consumer) -> {
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if (integer % 2 == 0) {
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consumer.accept(integer * (1 + percentage));
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}
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})
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.sum();
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assertThat(sum).isEqualTo(12.12, offset(0.001d));
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}
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@Test
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public void givenAListOfAlbums_whenFlatMap_thenGetListOfArtistAlbumPairs() {
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List<Pair<String, String>> artistAlbum = albums.stream()
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.flatMap(album -> album.getArtists()
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.stream()
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.map(artist -> new ImmutablePair<String, String>(artist.getName(), album.getAlbumName())))
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.collect(toList());
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assertThat(artistAlbum).contains(new ImmutablePair<String, String>("bob", "album1"), new ImmutablePair<String,
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String>("tom", "album1"), new ImmutablePair<String, String>("bill", "album2"), new ImmutablePair<String, String>("tom", "album2"));
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}
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@Test
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public void givenAListOfAlbums_whenMapMulti_thenGetListOfPairsOfArtistAlbum() {
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List<Pair<String, String>> artistAlbum = albums.stream()
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.<Pair<String, String>> mapMulti((album, consumer) -> {
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for (Artist artist : album.getArtists()) {
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consumer.accept(new ImmutablePair<String, String>(artist.getName(), album.getAlbumName()));
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}
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})
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.collect(toList());
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assertThat(artistAlbum).contains(new ImmutablePair<String, String>("bob", "album1"), new ImmutablePair<String, String>("tom", "album1"),
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new ImmutablePair<String, String>("bill", "album2"), new ImmutablePair<String, String>("tom", "album2"));
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}
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@Test
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public void givenAListOfAlbums_whenFlatMap_thenGetListOfArtistAlbumjPairsBelowGivenCost() {
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int upperCost = 9;
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List<Pair<String, String>> artistAlbum = albums.stream()
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.flatMap(album -> album.getArtists()
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.stream()
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.filter(artist -> upperCost > album.getAlbumCost())
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.map(artist -> new ImmutablePair<String, String>(artist.getName(), album.getAlbumName())))
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.collect(toList());
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assertTrue(artistAlbum.isEmpty());
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}
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@Test
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public void givenAListOfAlbums_whenMapMulti_thenGetListOfArtistAlbumPairsBelowGivenCost() {
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int upperCost = 9;
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List<Pair<String, String>> artistAlbum = albums.stream()
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.<Pair<String, String>> mapMulti((album, consumer) -> {
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if (album.getAlbumCost() < upperCost) {
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for (Artist artist : album.getArtists()) {
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consumer.accept(new ImmutablePair<String, String>(artist.getName(), album.getAlbumName()));
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}
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}
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})
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.collect(toList());
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assertTrue(artistAlbum.isEmpty());
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}
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@Test
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public void givenAListOfAlbums_whenMapMulti_thenGetPairsOfArtistMajorLabelsUsingMethodReference() {
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List<Pair<String, String>> artistLabels = albums.stream()
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.mapMulti(Album::artistAlbumPairsToMajorLabels)
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.collect(toList());
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assertThat(artistLabels).contains(new ImmutablePair<String, String>("bob:album1", "label1,label3"), new ImmutablePair<String, String>("tom:album1", "label2,label3"),
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new ImmutablePair<String, String>("bill:album2", "label2,label3"), new ImmutablePair<String, String>("tom:album2", "label2,label4"));
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}
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}

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