Checking for duplicates in a List of Objects C#

Question

I am looking for a really fast way to check for duplicates in a list of objects.

I was thinking of simply looping through the list and doing a manual comparison th

Answer 1

I like using this for knowing when there are any duplicates at all. Lets say you had a string and wanted to know if there was any duplicate letters. This is what I use.

string text = "this is some text";

var hasDupes = text.GroupBy(x => x).Any(grp => grp.Count() > 1);

If you wanted to know how many duplicates there are no matter what the duplicates are, use this.

var totalDupeItems = text.GroupBy(x => x).Count(grp =>  grp.Count() > 1);

So for example, "this is some text" has this...

total of letter t: 3

total of letter i: 2

total of letter s: 3

total of letter e: 2

So variable totalDupeItems would equal 4. There are 4 different kinds of duplicates.

If you wanted to get the total amount of dupe items no matter what the dupes are, then use this.

var totalDupes = letters.GroupBy(x => x).Where(grp => grp.Count() > 1).Sum(grp => grp.Count());

So the variable totalDupes would be 10. This is the total duplicate items of each dupe type added together.