Sets are good when you have a collection of things, the precise order isn't 
important to you, and you want to avoid duplicates.  I used one in some code 
recently where I wanted to maintain a collection of people who were co-authors 
in a Clojure patch, and the input file I started with could mention the same 
person's name multiple times.  I only wanted each person to be included once, 
no matter how many times they were mentioned in the patch file, and I didn't 
care about the order they appeared.

Sets are also a nice way to take another Clojure collection and eliminate 
duplicates -- just call (set coll) on the collection or sequence.

I haven't used them before, but if you want to avoid duplicates, and care about 
the order, sorted-set can be useful in some situations.

Andy

On Mar 23, 2012, at 7:47 AM, Leandro Oliveira wrote:

> Thank you for all replies.
> 
> The reason that I was using set instead of map was to use the functions from 
> closure.set. I like them.
> 
> But now I agree that map is a better approach. 
> 
> (select (fn [{:keys [id]}] (not= id 1)) xrel) is O(n). Right?
> 
> Can I say that if you need remove an item you should use a map?
> 
> What sets are good for?
> 
> leandro.

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