# [R] Need some help

jim holtman jholtman at gmail.com
Tue Oct 16 22:05:50 CEST 2007

```sum(toss == 1) /length(toss) # assuming heads == 1

On 10/16/07, azzza <azza.khogaliali at utoronto.ca> wrote:
>
>
> THANKYOU guyz! yes, Jim's code was right (it was similar to someone
> elses)....I somehow missed his reply!
> Yes, that was exactly what i was looking for. lastly, how do i find the
>
>
>
> Marc Schwartz wrote:
> >
> > On Tue, 2007-10-16 at 11:53 -0700, azzza wrote:
> >>
> >>
> >> ok, so suppose a coin is tossed 1000 times. Each time head occurs, we win
> >> a
> >> dollar, otherwise we lose a dollar. Let S(n) be our accumulated winnings
> >> after n tosses. For instance, if the sequence HHHTT occurs in the first
> >> five
> >> tosses, then S(5) = \$1.00 wheras if the sequence HTTTT occurs, S(5) =-\$3.
> >> So
> >> now, we want to see how many times during the 1000tosses S9n) will go
> >> from a
> >> positive balance to a negative balanc eor the other way around. So for
> >> our
> >> simulation, S(n) is computed by adding one to S(n-1) if a head occurs,
> >> and
> >> subtracting one form S(n-1) if a tail occurs. A change in sign will occur
> >> on
> >> the nth toss in one of two ways: S(n-2)=1, S(n-1)=0 and, S(n)= -1 OR
> >> S(n-2)
> >> = -1, S(n-1)=0 and S(n)=1. This is equivalent to S(n-2)+ S(n-1)+ S(n)=0.
> >> so now, n is the numbe rof tosses,  S(n) is the number of heads minus the
> >> number of tails in n tosses and C is the number of times S(n) changes
> >> sign.
> >> so we initialize n=0, S(-1)=0, S(0)=0, and C(0)=0
> >>
> >> now we should,
> >> -generate u, a uniform number, with the increment, n=n+1 ....(our n=1000)
> >> -if u<1/2, that is tails occur, set S(n)=S(n-1)-1, and also set
> >> S(n)=S(n-1)+1
> >> - If S(n) +S(n-1)+S(n-2)=0, then increment C=C+1.
> >>
> >> My issue is simulating this in R, where I need to code the number of sign
> >> changes, the frequency of heads, and to plot S(n) versus n in a line
> >> graph.
> >>
> >>
> >> for each coin toss, the number of sign changes could either be a positive
> >> number, zero, or a negative number.
> >
> > I believe that Jim had the right approach in his reply here:
> >
> >   https://stat.ethz.ch/pipermail/r-help/2007-October/143383.html
> >
> > and Prof. Koenker has given you a reference on the theory:
> >
> >   https://stat.ethz.ch/pipermail/r-help/2007-October/143385.html
> >
> > HTH,
> >
> > Marc
> >
> > ______________________________________________
> > R-help at r-project.org mailing list
> > https://stat.ethz.ch/mailman/listinfo/r-help
> > http://www.R-project.org/posting-guide.html
> > and provide commented, minimal, self-contained, reproducible code.
> >
> >
>
> --
> View this message in context: http://www.nabble.com/Need-some-help-tf4624513.html#a13241118
> Sent from the R help mailing list archive at Nabble.com.
>
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> and provide commented, minimal, self-contained, reproducible code.
>

--
Jim Holtman
Cincinnati, OH
+1 513 646 9390

What is the problem you are trying to solve?

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