[Jprogramming] Closest local minimums of data

[Mike Day]

I was drafting this before Oleg's reply arrived.  It's slightly
different from his, and shows a derivation of a tacit form.
==============================================================
Is this the sort of thing you need? 
Consider:
   d
10 7 5 6 7 1 9 8 2 4
   (1 , 2 >/\ ])d NB. boolean for = left > right for each pair ?
1 1 1 0 0 1 0 1 1 0

   1 1 1 0 0 1 0 1 1 0 < ;. 1 d  NB. partition d by this boolean
+--+-+-----+---+-+---+
|10|7|5 6 7|1 9|8|2 4|
+--+-+-----+---+-+---+
   1 1 1 0 0 1 0 1 1 0(<&(<./\);. 1)d NB. required work in boxes
+--+-+-----+---+-+---+
|10|7|5 5 5|1 1|8|2 2|
+--+-+-----+---+-+---+

   1 1 1 0 0 1 0 1 1 0 ;@(<&(<./\);. 1)d NB. unbox
10 7 5 5 5 1 1 8 2 2

   ((1,2>/\]);@(<&(<./\);. 1)])d NB. tacit form
10 7 5 5 5 1 1 8 2 2

   (;@(<&(<./\);. 1)~1,2>/\])d  NB. tacit avoiding one "]" 
10 7 5 5 5 1 1 8 2 2

Mike

Mikl Kurkov wrote:

> I need function that for each value in vector return this value if  
> previous was bigger and return closest minimum if previous data is 
> lesser.
>
> Examlpe:
>
> d =: 10 7 5 6 7 1 9 8 2 4 NB. data
> r =: 10 7 5 5 5 1 1 8 2 2 NB. result
>
> NB. What I have now is
> fn1 =:  ({:@])`[ @. ( [ < {.@])
> fn2 =:  [ , }.@] , fn1
> fn  =:  (}. @: (fn2/) @:(,{:)@: |.) f.
>
> r -: fn d
> 1
>
> But it realy slow and I think it could be optimized.
> So what would you suggest?
>
> Thanks in advance.
>