[R] Need some help

[azzza]

Thats what is frustrating me....I've done a lot of reading, but there doesnt
seem to be much info on sign changes..............I  dont udnerstand why the
poportion of sign changes is much less than 50%, despite the proportion of
heads being equal to that of tails. 


Marc Schwartz wrote:
> 
> You might want to do some more research on "Bernoulli Trials" and "Fair
> Coins", which would provide some enlightenment on why you would not
> "expect" 500 sign changes in 1,000 tosses and why you should, if the
> coin is "fair", expect to *approach* a 50/50 distribution of heads and
> tails in a large number of tosses, but not actually observe it.
> 
> HTH,
> 
> Marc Schwartz
> 
> 
> On Tue, 2007-10-16 at 09:05 -0700, azzza wrote:
>> 
>> You are right, I was a bit too vague. I am trying to simulate 1000 coin
>> Tosses. Then to write a code for the number of heads/Tails.....naturally,
>> we
>> would expect the proportion of heads to be 50% so the number of heads
>> would
>> be around 500. Secondly, I'm trying to look at the number of sign changes
>> in
>> 1000 tosses. The example in the book shows that the number of sign
>> changes
>> is WAY less than 50%. so I was  trying to look for a code that shows the
>> number of sign changes, which someone pointed out would be to use
>> rle(x).....my concern however is that when the rle(x) is used, the
>> proportion of sign changes is about 50% (around 500), which would be
>> logical
>> to expect, however, real life experiments have shown that the number of
>> sign
>> changes is actually much less than 50%. The other thing I was trying to
>> do
>> is to plot a line graph of number of sign changes versus the number of
>> tosses. Yes, the number of tosses should begin at zero, and at zero coin
>> toss, the sign change is zero. The range of the number of sign changes in
>> the Y-axis should include negative values of Y. So, for toss number zero,
>> the sign change is 0, for the first toss, the sign change may be +3 for
>> instance, for the 50th toss, the sign change may be -5 for instance. The
>> plot shown in the book shows that for most of the tosses, the sign
>> changes
>> were negative, and this would explain how the overall number of sign
>> changes
>> is very low.
>> 
>> so basically, i was looking for a code to show the number of sign
>> changes, 
>> and a plot of sign changes versus toss number (from toss #0 to toss
>> number
>> 1000). The Y axis (number of sign changes, should include negative values
>> of
>> Y)
>> 
>> thanks
>> 
>> 
>> 
>> Daniel Nordlund wrote:
>> > 
>> >> -----Original Message-----
>> >> From: r-help-bounces at r-project.org
>> [mailto:r-help-bounces at r-project.org]
>> >> On Behalf
>> >> Of azzza
>> >> Sent: Monday, October 15, 2007 6:06 PM
>> >> To: r-help at r-project.org
>> >> Subject: Re: [R] Need some help
>> >> 
>> >> 
>> >> 
>> >> Thanks Jholtman.
>> >> However, the plot didnt come out the way I envisone dit to be. On the
>> Y
>> >> axis, i should have sign changes in 1000 tosses, the range being from
>> >> negative to postitive, and a straight horizontal line across  y=0. The
>> >> X-axis should have the toss number, range 0-1000
>> >> 
>> > 
>> > You would probably get more prompt and useful help if you would provide
>> a
>> > small, self- contained example of what you wanted (maybe small enough
>> that
>> > you could work it by hand).  Also, if you provided some code using the
>> > help that you have already received, that would show that you are
>> trying
>> > to solve the problem yourself and others could help with the specific R
>> > program issues that you are having.  For example, it is not clear to me
>> if
>> > you want to count the first run of tosses as 0 or 1 sign change.  I
>> will
>> > assume it is zero.  So with that assumption, does this get you what you
>> > want?
>> > 
>> > n <- 1000
>> > x <- sample(c(0,1), n, TRUE)
>> > y <- rle(x)
>> > 
>> > z <- rep(1:length(y$lengths),y$lengths)
>> > plot(1:n,z-1)
>> > 
>> > Hope this is helpful,
>> > 
>> > Dan
>> > 
>> > Daniel Nordlund
>> > Bothell, WA USA
>> > 
>> > ______________________________________________
>> > R-help at r-project.org mailing list
>> > https://stat.ethz.ch/mailman/listinfo/r-help
>> > PLEASE do read the posting guide
>> > http://www.R-project.org/posting-guide.html
>> > and provide commented, minimal, self-contained, reproducible code.
>> > 
>> > 
>>
> 
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
> 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#a13238567
Sent from the R help mailing list archive at Nabble.com.