I want to remove duplicate rows from a matrix. I read How can I remove duplicates in an array but keep the same order?, but this is not exactly what I want.

The solution above removes duplicate values (cells) from matrix (and returns a vector), but I need to remove duplicate rows and return a matrix — the same matrix without duplicate rows.

Example: 

a = [1,2; 3,4; 5,6; 1,2; 7,8]

a =
     1     2
     3     4
     5     6
     1     2
     7     8

%...

ans =
     1     2
     3     4
     5     6
     7     8

The order doesn't matter. 

Answers: 

See http://www.mathworks.com/help/techdoc/ref/unique.html

b = unique(A, 'rows') returns the unique rows of A. 

Here is my solution 

 

package com.test;

import java.util.Arrays;
import java.util.HashSet;
import java.util.Iterator;
import java.util.Set;

public class DuplicateInMatrix {
    public static void main(String[] args) {
        Integer[][] arr = { { 1, 2, 3 }, { 4, 5, 6 }, { 1, 2, 3 } };
        Set set = new HashSet<>();
        for (int i = 0; i < arr.length; i++) {
            set.add(new Element(arr.length, arr[i]));
        }

        buildResultArray(set);
    }

    private static void buildResultArray(Set set) {
        Integer[][] arr = new Integer[set.size()][];
        Iterator itr = set.iterator();
        for (int i = 0; i < arr.length && itr.hasNext(); i++) {
            arr[i] = itr.next().row;
        }
        printArrray(arr);
    }

    private static void printArrray(Integer[][] arr) {

        for (int i = 0; i < arr.length; i++) {
            for (int j = 0; j < arr[i].length; j++) {
                System.out.print(arr[i][j] + " ");
            }
            System.out.println();
        }
    }

    static class Element {
        int n;
        Integer[] row = new Integer[n];

        public Element(int n, Integer[] row) {
            this.n = n;
            this.row = row;
        }

        @Override
        public int hashCode() {
            return Arrays.hashCode(row);
        }

        @Override
        public boolean equals(Object obj) {
            if (this == obj)
                return true;
            if (obj == null)
                return false;
            if (getClass() != obj.getClass())
                return false;
            Element other = (Element) obj;
            return Arrays.deepEquals(this.row, other.row);
        }

        @Override
        public String toString() {
            return Arrays.toString(row);
        }
    }
}