41 lines
1.2 KiB
Java
41 lines
1.2 KiB
Java
import java.util.*;
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public class HashJoin {
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public static void main(String[] args) {
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String[][] table1 = {{"27", "Jonah"}, {"18", "Alan"}, {"28", "Glory"},
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{"18", "Popeye"}, {"28", "Alan"}};
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String[][] table2 = {{"Jonah", "Whales"}, {"Jonah", "Spiders"},
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{"Alan", "Ghosts"}, {"Alan", "Zombies"}, {"Glory", "Buffy"},
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{"Bob", "foo"}};
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hashJoin(table1, 1, table2, 0).stream()
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.forEach(r -> System.out.println(Arrays.deepToString(r)));
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}
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static List<String[][]> hashJoin(String[][] records1, int idx1,
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String[][] records2, int idx2) {
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List<String[][]> result = new ArrayList<>();
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Map<String, List<String[]>> map = new HashMap<>();
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for (String[] record : records1) {
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List<String[]> v = map.getOrDefault(record[idx1], new ArrayList<>());
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v.add(record);
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map.put(record[idx1], v);
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}
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for (String[] record : records2) {
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List<String[]> lst = map.get(record[idx2]);
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if (lst != null) {
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lst.stream().forEach(r -> {
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result.add(new String[][]{r, record});
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});
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}
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}
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return result;
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}
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}
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