
Thanks Gabor.

On Wed, Jul 28, 2010 at 9:24 PM, Gabor Grothendieck [via R] <
ml-node+2305561-610338075-309606@n4.nabble.com<ml-node%2B2305561-610338075-309606@n4.nabble.com>
> wrote:

> On Wed, Jul 28, 2010 at 2:10 PM, Raghu <[hidden email]<http://user/SendEmail.jtp?type=node&node=2305561&i=0>>
> wrote:
>
> > Hi
> >
> > I have say a large vector of 3500 digits. Initially the digits are 0s and
>
> > 1s. I need to check for a rule to change some of the 0s to -1s in this
> > vector. But once I change a 0 to -1 then I need to start applying the
> rule
> > to change the next 0 only after I see the next 1 in the vector.
> >
> > Say for example x = (0,0,0,0,0,0,0,1,0,0,1,1,0,0,1,0,0,0,1)
> > I need to traverse from the 9th element to the last ( because the first
> > occurrence of 1 is at 8) . Let us assume that according to our rule we
> > change the 13th element (only 0s can be changed) to -1. Now we need to go
> to
> > the next occurrence of 1 (which is 15) and begin the rule application
> from
> > the 16th till the end of the vector and once replaced a 0 to a -1 then
> start
> > again from the next 1. How do we code this? I 'feel' recursion is the
> best
> > possible solution but I am not a programmer and will await experts'
> views.
> > If this is not a typical R-forum question then my advance apologies.
> >
>
> If you are asking to replace the first 0 after any string of 1s with a
> -1 then try this:
>
>
> > replace(x, c(FALSE, diff(x) < 0), -1)
>  [1]  0  0  0  0  0  0  0  1 -1  0  1  1 -1  0  1 -1  0  0  1
>
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-- 
'Raghu'

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