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Removing Duplicates from an Array (Using C#)

Sung M. Kim on March 18, 2017

* Featured Image – “removed.jpg” by Don Crowley, used under BY SA This article is from last year but after reading Sai's article, ...
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Sai gowtham •

Do you have any solution for removing duplicate objects from an array?

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Sung M. Kim •

I haven't implemented any but the implementation can be a bit tricky for the case 1 & 2.1

Case 1 & 2.1

  • Implement IComparable interface for instance of the class you are comparing. So that you can compare current & next objects in an array.
  • Also override the comparison operators (>, >=, <, <=).
// To enable Point class object instance comparable.
public class Point : IComparable<Point>
{
    public int CompareTo(Point otherPoint)
    {
        return this.X > otherPoint.X && this.Y > otherPoint.Y;
    }

    public static bool operator >  (Point p1, Point p2) => p1.CompareTo(p2) == 1;
    public static bool operator <  (Point p1, Point p2) => p1.CompareTo(p2) == -1;
    public static bool operator >=  (Point p1, Point p2) => p1.CompareTo(p2) >= 0;
    public static bool operator <=  (Point p1, Point p2) p1.CompareTo(p2) <= 0;
}
...

// case 1
if (a[i] != a[i + 1])
{
    result.Add(a[i]);
}

// case 2.1
if (!alreadySeen.Contains(item))
    alreadySeen.Add(item);

For Case 2.2

Create a class implementing IComparer interface so that you can specify how objects can be sorted.

public class PointComparer<Point> : IComparer<Point>
{
  int IComparer.Compare(Point p1, Point p2)  
  {
      return p1.X > p2.X && p1.Y > p2.Y;
  }
}

// ...
Array.Sort(points, new PointComparer());