okay, new take solving the issue raised by Mark:

(defn uniquify [in format-fn]
  (loop [[item :as in] (seq in)
         {n item :as item-nbrs} {}
         out []]
    (if-not in
      out
      (let [format-fn (if n format-fn (constantly item))
            new-item (format-fn item n)]
        (recur (next in)
               (merge-with (fnil + 0)
                           item-nbrs
                           (hash-map item 1 new-item 1))
               (conj out new-item))))))

=> (uniquify ["a" "b" "c" "a" "a_1" "a_1" "a"] #(str %1 "_" %2))
["a" "b" "c" "a_1" "a_1_1" "a_1_2" "a_2"]



2014/1/10 Colin Yates <colin.ya...@gmail.com>

> Gosh - my public humiliation continues.  Here is one that actually works:
>
> (first (reduce (fn [[results seen] item]
>                       (let [cnt (get seen item 0)]
>                         [(conj results (if (> cnt 0) (format-fn item cnt)
> item))
>                          (assoc seen item (inc cnt))]))
>                     [[] {}]
>                     items))
> (fact "strings can be made unique"
>   (s/uniquify ["a" "b" "c"]) => ["a" "b" "c"]
>   (s/uniquify ["a" "b" "a" "c" "b" "b" "b" "b" "a"]) => ["a" "b" "a_1" "c"
> "b_1" "b_2" "b_3" "b_4" "a_2"])
>
> On Friday, 10 January 2014 20:59:00 UTC, Colin Yates wrote:
>>
>> Sorry - wrong c/p:
>>
>> (first (reduce (fn [[results seen] item]
>>                       (let [cnt (get seen item 0)
>>                             item (if (> cnt 0) (format-fn item cnt) item)]
>>                         [(conj results item) (assoc seen item (inc
>> cnt))]))
>>                     [[] {}]
>>                     items))
>>
>> On Friday, 10 January 2014 20:55:04 UTC, Colin Yates wrote:
>>>
>>> I thought I would have a go myself without copying (although having read
>>> them earlier) the other functions and this is what I came up with:
>>>
>>> (first (reduce (fn [[results seen] item]
>>>                       (let [occurrences ((fnil identity 0) (get seen
>>> item))
>>>                             seen (assoc seen item (inc occurrences))
>>>                             item (if (> occurrences 0) (format-fn item
>>> occurrences) item)]
>>>                         [(conj results item) seen])) [[] {}] (seq
>>> items)))
>>>
>>> This doesn't solve the problem you mention, but baby steps.
>>>
>>> Being really anal I could claim the original a_2 should remain a_2 and
>>> the third instance of a jump to being a_3.  I thought about this and
>>> couldn't see how to do this with reduce because I really want to say "oh, I
>>> have a new name, recurse into the function again with the new proposed
>>> name", i.e. loop the generation of the proposed name until it is unique,
>>> but I haven't got that far yet (without potentially blowing the stack!)
>>>
>>> Then I saw your 'recur' used outside of a loop which points the way...
>>>
>>> Thanks!
>>>
>>> On Friday, 10 January 2014 20:16:28 UTC, puzzler wrote:
>>>>
>>>>
>>>> On Fri, Jan 10, 2014 at 11:52 AM, Colin Yates <colin...@gmail.com>wrote:
>>>> > way to take the wind out of our sails!  Well spotted :).
>>>>
>>>>
>>>> It's not too hard to fix.   Here's an adapted version of Jonas'
>>>> solution that should do the trick:
>>>>
>>>> (defn uniqueify [items]
>>>>   (first
>>>>     (reduce (fn [[results count-map] item]
>>>>               (let [n (count-map item 0)]
>>>>                 (if (zero? n)
>>>>                   [(conj results item) (assoc count-map item (inc n))]
>>>>                   (recur [results (assoc count-map item (inc n))]
>>>>                          (str item \_ n)))))
>>>>             [[] {}]
>>>>             items)))
>>>>
>>>> => (uniqueify ["a" "a" "a" "a" "b" "a_2" "a_3" "a_3_1" "a_3_1" "a"])
>>>> ["a" "a_1" "a_2" "a_3" "b" "a_2_1" "a_3_1" "a_3_1_1" "a_3_1_2" "a_4"]
>>>>
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