I have a list of text strings: ["Alice", "Bob", "Cindy", "Bob", "Bob", "Dave", "Cindy"] As you can see, some of the strings occur only once; others appear two or more times. I would like to end up with a new list, according to the following rules: 1) If a string occurs only once in the original list, then that string appears unchanged in the new list. 2) If a string occurs more than once in the original list, then each occurrences of that string is "decorated" with a numerical suffix indicating its relative position among its peers. In the case of the above list, the result of applying these rules would be: ["Alice", "Bob:1", "Cindy:1", "Bob:2", "Bob:3", "Dave", "Cindy:2"] So, how do we do this? The straightforward approach is to traverse the list twice, once to build a table of repeat counts for the different strings, and a second time to generate the new list, based on the old list plus the table of repeat counts. Of course, it's possible to streamline this into a single traversal by building up a list of thunks at the same time as the table of repeat counts is generated, and then to resolve those thunks by applying them in one fell swoop to the table. But while this does _conceptually_ streamline the problem, it doesn't offer any practical improvement; it takes at least as much processing effort to resolve the thunks as it would to make a second pass through the list. Can we do better? I can't think of a way to do better, and my gut feeling is that there isn't one (in general, it's impossible to know whether the first element of the new list will be "Alice" or "Alice:1" until the entire original list has been traversed), but I thought I'd put the question out to the community to see if anyone had any brilliant insights. Steve Schafer Fenestra Technologies Corp. http://www.fenestra.com/