Re: another vectorization challenge

[Jaroslav Hajek]

On Fri, Aug 27, 2010 at 3:36 AM, Tim Rueth <address@hidden> wrote:
> For those of you who like to solve vectorization problems, I'm stuck on the
> following:
>
> Let's say I have a vector with values that range from -10 to 10:
>
> cpg_v = 20*rand(1,n) - 10;
>
> Now, I want to create another vector cr_v of the same size with the
> following logic:
>
> Whenever cpg_v drops below "cr_thd," then cr_v should get a 1.  Okay, that's
> easy:
>
> cr_v = zeros(1,length(cpg));
> cr_v (cpg_v < cr_thd) = 1;
>
> I also want to know when cpg_v goes back above "rec_thd."  That's easy, too:
>
> rec_v (cpg_v > rec_thd) = 1;
>
> But here's the tricky part:  Reading cpg_v from 1:end, once a "1" is
> encountered at the corresponding location in cr_v, then cr_v should be
> assigned a "2" after that location (unless cpg_v drops below cr_thd
> again) until the point where cpg_v is greater than "rec_thd."  Note that a
> "2" shouldn't be assigned until there's a 1 in cr_v, and the run of 2's
> should stop once a 1 is encountered in rec_v.  Here's a simple example (with
> cr_thd = -4, rec_thd = 4), and the desired output:
>

I usually like to help, but I don't understand your tricky part
description. If I did, 4th column should end with 2's.

>     cpg_v        cr_v        rec_v    desired cr_v
> -------------------------------------------------------------------
>    6.45824   0.00000   1.00000   0.00000
>    7.42197   0.00000   1.00000   0.00000
>   -2.41237   0.00000   0.00000   0.00000
>    4.85508   0.00000   1.00000   0.00000
>    3.78177   0.00000   0.00000   0.00000
>   -3.24793   0.00000   0.00000   0.00000
>   -5.63435   1.00000   0.00000   1.00000
>   -2.10278   0.00000   0.00000   2.00000
>   -0.80376   0.00000   0.00000   2.00000
>    7.97556   0.00000   1.00000   0.00000
>   -5.11177   1.00000   0.00000   1.00000
>   -4.56460   1.00000   0.00000   1.00000
>   -8.43245   1.00000   0.00000   1.00000
>    4.85563   0.00000   1.00000   0.00000
>   -2.17610   0.00000   0.00000   0.00000
>    4.87113   0.00000   1.00000   0.00000
>    6.78267   0.00000   1.00000   0.00000
>    9.30517   0.00000   1.00000   0.00000
>    5.31377   0.00000   1.00000   0.00000
>   -4.93238   1.00000   0.00000   1.00000
>    2.10757   0.00000   0.00000   2.00000
>    6.94569   0.00000   1.00000   0.00000
>    1.67053   0.00000   0.00000   0.00000
>   -7.23665   1.00000   0.00000   1.00000
>   -5.43656   1.00000   0.00000   1.00000
>   -9.79481   1.00000   0.00000   1.00000
>    0.45726   0.00000   0.00000   2.00000
>   -2.14684   0.00000   0.00000   1.00000
>   -0.75054   0.00000   0.00000   1.00000
>   -2.59986   0.00000   0.00000   1.00000
> Obviously, this is easy to do in a for-loop, but is there a way to do it
> just with vectors?
>

If you can do it with a for loop, why don't you post it here? Not only
that can clarify your intent, but can also serve as an alternative
code to check against.

regards

-- 
RNDr. Jaroslav Hajek, PhD
computing expert & GNU Octave developer
Aeronautical Research and Test Institute (VZLU)
Prague, Czech Republic
url: www.highegg.matfyz.cz