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Re: lookback function? or instlookback?
From: |
abl5 |
Subject: |
Re: lookback function? or instlookback? |
Date: |
Fri, 2 Dec 2005 07:07:14 -0500 (EST) |
On Thu, 1 Dec 2005, Francesco Potorti` wrote:
> >-Take two specific vectors of data, say I and J
> >-Start two counters at the first element. One increments by one every row
> >(until reset) and the other increments by 1 when either
> > --there is a non-zero difference between the current non-zero
> >value of I and the most recent previous non-zero value of I
> > or
> > --the same is true for J
> >The other challenge is that both I and J change their non-zero values at
> >the same time, but because only I or J is non-zero in a given row, I also
> >have to figure out how to tell the counters to reset & increment for the
> >first of those two changes but not for the second.
>
> It seems to me that the two statements
> - both I and J change their non-zero values at the same time
> - only I or J is non-zero in a given row
> are contradictory, so I don't understand what you want to do.
Ok. Here is a sample matrix:
I J
0 20
0 20
40 0
0 20
40 0 <<between this row and the next, values are changed for I & J
20 0
0 40
etc...
>
> Anyway, if I have understood anything, this kind of things can be done
> using combinations of the functions cumsum, diff and find, possibly with
> the help of prepad and postpad.
ok, thanks.
Arwen
>
> --
> Francesco Potortì (ricercatore) Voice: +39 050 315 3058 (op.2111)
> ISTI - Area della ricerca CNR Fax: +39 050 313 8091
> via G. Moruzzi 1, I-56124 Pisa Email: address@hidden
> Web: http://fly.isti.cnr.it/ Key: fly.isti.cnr.it/public.key
>
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