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: [EMAIL PROTECTED] >> [mailto:[EMAIL PROTECTED] >> >> On Behalf >> >> Of azzza >> >> Sent: Monday, October 15, 2007 6:06 PM >> >> To: r-help@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@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@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. ______________________________________________ R-help@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.
