On Tue, Jan 17, 2012 at 3:46 PM, Dennis Haupt <[email protected]> wrote:
> after the "wtf"s have worn off a bit, go on reading.
> imagine a simple problem: you have a collection of numbers and you have
> to write a function which collects all the numbers that are contained
> uneven times. for example, for a collection (1,2,3,2,3,4) the correct
> result is (1,4)
>
> ask a child:
> "you just make pairs and return the leftovers"
>
> ask a non-child human:
> "count how often a number is in the list and pick the ones that are
> contained uneven times"
>
> i also asked some oo programmers. one of the answers involved a
> multimap, building it, iterating over it again and putting the result in
> a new list. one answer was "i don't see any purpose in this".
> there was no FP coder around at that time.
FWIW,
(defn odd-occurrences [x]
(map first
(filter
(fn [[_ v]] (odd? v))
(frequencies x))))
Signed,
An FP coder
:)
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