Here's the first example from the clojure docs for partition-by:
{ 1 2 3 4 5 } [ [ 3 = not ] bi@ and ] monotonic-split
{ { 1 2 } { 3 } { 4 5 } }
Also you could do this if the function is expensive so you only apply it
once:
{ 1 2 3 4 5 } [ 3 = ] map-zip [ [ second ] bi@ = ] monotonic-split [ keys ]
map .
{ { 1 2 } { 3 } { 4 5 } }
The second example is
{ 1 1 1 2 2 3 3 } [ nip odd? ] monotonic-split .
{ { 1 1 1 } { 2 2 } { 3 3 } }
Cheers,
Doug
On Wed, Dec 4, 2019 at 3:07 PM <pet...@riseup.net> wrote:
> Just like last year I'm working through Advent of Code challenges. Jus
> like last year I'm probably going to fall out in the next day or two :)
> Nevertheless, I'm still holding up, and have a question.
>
> The 4th day part 2 quest has a test, semi-quoting: two adjacent matching
> digits that are not part of a larger group of matching digits. So 112 is
> fine (two 1's) but 111 is not. Also 11122 is fine, we're just looking
> for any occurrence of two adjacent matching digits.
>
> I write some clojure in my day job and there's this function
> partition-by[1]. With a word like that the check could simply be
>
> digits [ ] partition-by [ length 2 = ] any?
>
> where digits explodes the number into a vector of its digits.
>
> Alas, I couldn't find such a word and after a lot of looking around
> nothing similar. Grouping and clumping and such didn't lead me to any
> simple solution, so I just rolled something dirty:
>
> : -reset ( cnt curr next -- one next ) [ 2drop 1 ] dip ;
> : -inc ( cnt curr next -- cnt+1 curr ) drop [ 1 + ] dip ;
> : -init ( seq -- cnt curr seq ) [ 1 ] dip unclip-slice swap ;
> : has-2? ( seq -- ? ) -init [ 2dup = not [ pick 2 = [ ] [ -reset f ]
> if ] [ -inc f ] if ] find [ 2drop 2 = ] dip or ;
>
> I was thinking about writing partition-by myself but I don't like using
> locals and I just wasn't able to come up with a simple solution on the
> stack.
>
> Thoughts/pointers welcome!
>
> P.S.: if anyone wants to see/compare/review my solutions so far I can
> post it somewhere, just let me know.
>
>
> [1] https://clojuredocs.org/clojure.core/partition-by
>
> --
> ------------
> Peter Nagy
> ------------
>
>
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