Last Updated: February 25, 2016

Using LINQ Aggregate effectively

I had some trouble figuring out how to use LINQ's aggregate,
one of the reasons is that I didn't find any good references on the net.

The problem solved; calculate the union between an arbitrary number of Rectangles

This was something I did at work recently when working on a image analysis program.

In the following, I will show 3 pieces of code doing just that in 3 different ways

One code piece using a loop
One code piece using a recursive function (mostly for the fun of it)
And Lastly a LINQ Expression using Aggregate

I think the examples will help illuminate how the LINQ expression works.

Using a loop

static Rectangle GetRectUnionLoop(params Rectangle[] rectangles)
{
 if (rectangles.Length == 0)
 return Rectangle.Empty;

 Rectangle boundingBox = rectangles[0];
 foreach (var rectangle in rectangles) 
 {
 boundingBox = Rectangle.Union(boundingBox, rectangle);

 }
 return boundingBox;
}

Using a recursive function

static Rectangle GetRectUnionRecursive(params Rectangle[] rectangles)
{
 return (rectangles.Length > 1)
 ? Rectangle.Union(rectangles[0],
 GetRectUnionRecursive(rectangles.Skip(1).ToArray()))
 : (rectangles.Length == 1)
 ? rectangles[0]
 : Rectangle.Empty;
}

Using LINQ

static Rectangle GetRectUnionLINQ(params Rectangle[] rectangles)
{
 return (rectangles.Length == 0)
 ? Rectangle.Empty
 : rectangles
 .Aggregate(rectangles[0], (acc, rect) => Rectangle.Union(acc, rect));
}

#.net

#linq

#c#