Intersect and Union in byte array of 2 files

Question

I have 2 files. 1 is Source File and 2nd is Destination file.

Below is my code for Intersect and Union two file using byte array.

FileStream frsrc = new FileStream("Src.bin", FileMode.Open);
FileStream frdes = new FileStream("Des.bin", FileMode.Open);
int length = 24; // get file length
byte[] src = new byte[length];
byte[] des = new byte[length]; // create buffer
int Counter = 0;   // actual number of bytes read
int subcount = 0;

while (frsrc.Read(src, 0, length) > 0)
{
    try
    {
        Counter = 0;
        frdes.Position = subcount * length;
        while (frdes.Read(des, 0, length) > 0)
        {                               
                var  data = src.Intersect(des);                          
                var data1 = src.Union(des);                               
                Counter++;                               
        }        
        subcount++;
        Console.WriteLine(subcount.ToString());
        }
    }
    catch (Exception ex)
    {                          
    }
}

It is works fine with fastest speed. but Now the problem is that I want count of it and when I Use below code then it becomes very slow.

  var  data = src.Intersect(des).Count();                          
  var  data1 = src.Union(des).Count();

So, Is there any solution for that ? If yes,then please lete me know as soon as possible. Thanks

Answer 1

Intersect and Union are not the fastest operations. The reason you see it being fast is that you never actually enumerate the results!

Both return an enumerable, not the actual results of the operation. You're supposed to go through that and enumerate the enumerable, otherwise nothing happens - this is called "deferred execution". Now, when you do Count, you actually enumerate the enumerable, and incur the full cost of the Intersect and Union - believe me, the Count itself is relatively trivial (though still an O(n) operation!).

You'll need to make your own methods, most likely. You want to avoid the enumerable overhead, and more importantly, you'll probably want a lookup table.