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Re: split again


On Feb 23, 1:48 am, Arkadiusz.Ma... at gmail.com wrote:
> Hi,
>
> Thank you very much for your help in my provious post. Now, consider
> please a list
>
> z=Table[Random[],{1000}];
>
> zSplit=Split[z,#1<=0.7 === #2>=0.7];           (bulit thanks to your
> help)
>
> I want to pick the first sublist of zSplit that consists of elements
> <= 0.7 and whose length is greater than a certain number (say 5). I
> think that a good candidate would be using Cases and variations of _ ,
> but I don't know how.
>
> What I want to do (and what my both posts are about) is to find the
> first sublist of z with all elements less than A and the length of
> this sublist must be greater than B. Maybe there exists better
> solution than to Split z in advance since what I need to do in my next
> step is to find ONLY the FIRST sublist of splitted z.
>
> Thanks again,
>
> Arek

SeedRandom[2]; z = Table[Random[],{20}]

{0.238705,0.844529,0.473928,0.421515,0.512692,
 0.0228035,0.529257,0.0507012,0.74907,0.632356,
 0.0725195,0.251276,0.902785,0.672727,0.419794,
 0.512577,0.404555,0.00984124,0.168643,0.50482}

A = .7; B = 5;
n = Flatten[Position[isplit = Split@UnitStep[z - A],
    _?(Length@# > B && First@# == 0&), {1}, 1]/.{}->{0}][[1]]

3

If no run exists with the desired properties then n will be 0.
Otherwise, n is the position in isplit of the desired run, and

Length@Flatten@Take[isplit,n-1] + {1, Length@isplit[[n]]}

{3,8}

gives the first & last positions of the run in z.



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