[Haskell-cafe] Re: Data.Map: Enumerating ordered subset of keys

Jared Updike jupdike at gmail.com
Mon Feb 9 02:02:37 EST 2009

It looks like two "Map.split"s will do what I need except for allowing
more exact testing of <= vs. < (since == elements are left out of both


On 2/8/09, Jared Updike <jupdike at gmail.com> wrote:
> I would like to enumerate a subset of keys in a Map satisfying \ key
>  >= key1 && key <= key2 but in the expected, reasonable amount of time
>  (e.g. < O(log(n)) + O(m) for n total keys and m keys in the subset).
>  (Or key > key1 and/or key < key2 or some such combination).
>  Is there an appropriate idiom or combination of library functions to
>  accomplish this, short of digging into the code for Data.Map and
>  writing such a function for a forked version of Data.Map?
>  For example I could try something like a Set.split of a Set.split of
>  Map.keysSet of my original map, but will laziness magically do what I
>  really want? which is to walk down the tree to key1 (or the nearest
>  key > key1) and enumerate keys in order until key2 is reached?
>  Data.Map almost looks like what I need if I can do this.
>   Jared.

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