Uniquify Names in a list of objects with a Name property, by appending _2, _3, etc.

gistfile1.txt

class foo
{
	public string Name { get; set; }
	public string description { get; set; }
}

void Main()
{
	List<foo> coll = new List<foo>();
	coll.Add(new foo() { Name = "ross", description = "me" });
	coll.Add(new foo() { Name = "joel", description = "also me" });
	coll.Add(new foo() { Name = "ross", description = "me #2" });
	coll.Add(new foo() { Name = "ross", description = "me #3" });
	coll.Add(new foo() { Name = "joel", description = "also me #2" });
	
  // coll now contains the equivalent of this:
  // { {"Name": "ross", "Description": "me"}
  //   {"Name": "joel", "Description": "also me"}
  //   {"Name": "ross", "Description": "me #2"}
  //   {"Name": "ross", "Description": "me #3"}
  //   {"Name": "joel", "Description": "also me #2"} }

	coll.GroupBy(c => c.Name.ToUpperInvariant())
		.Select(g => g.Select((c, j) => new { foo = c, Name = (j == 0 ? c.Name : ($"{c.Name}_{j + 1}")) }))
		.SelectMany(g => g)
		.All(t => { t.foo.Name = t.Name; return true; });

// Note that no extra variables are defined, nor are any ToList() needed.
// There's also no need to track the original order, because we are modifying the original objects stored in the List!

 // coll now contains the equivalent of this:
  // { {"Name": "ross",  "Description": "me"}
  //   {"Name": "joel",  "Description": "also me"}
  //   {"Name": "ross2", "Description": "me #2"}
  //   {"Name": "ross3", "Description": "me #3"}
  //   {"Name": "joel2", "Description": "also me #2"} }
 

}