I don't think I can. For the sample data
d <- data.frame(x=c(1, 4, 9, 12), s=c(109, 1200, 5325, 8216)) when x = 4, s = 1200. However, that s4 is sum of y1 + y2 + y3 + y4. Wouldn't I have to know the y for x = 2 and x = 3 to get the value of y for x = 4? In the previous message, I created two sample data frames. d is what I'm trying to use to create df. I only know what's in d, df is just used to illustrate what I'm trying to get from d. robbie On Tue, May 22, 2012 at 12:30 PM, R. Michael Weylandt < michael.weyla...@gmail.com> wrote: > But if I understand your problem correctly, you can get the y values > from the s values. I'm relying on your statement that "s is sum of the > current y and all previous y (s3 = y1 + y2 + y3)." E.g., > > y <- c(1, 4, 6, 9, 3, 7) > > s1 = 1 > s2 = 4 + s1 = 5 > s3 = 6 + s2 = 11 > > more generally > > s <- cumsum(y) > > Then if we only see s, we can get back the y vector by doing > > c(s[1], diff(s)) > > which is identical to y. > > So for your data, the underlying y must have been c(109, 1091, 4125, > 2891) right? > > Or have I completely misunderstood your problem? > > Michael > > On Tue, May 22, 2012 at 12:25 PM, Robbie Edwards > <robbie.edwa...@gmail.com> wrote: > > Actually, I can't. I don't know the y values. Only the s and only for a > > subset of the data. > > > > Like this. > > > > d <- data.frame(x=c(1, 4, 9, 12), s=c(109, 1200, 5325, 8216)) > > > > > > > > On Tue, May 22, 2012 at 11:57 AM, R. Michael Weylandt > > <michael.weyla...@gmail.com> wrote: > >> > >> You can reconstruct the y values by taking first-differences of the s > >> vector, no? Then it sounds like you're good to go > >> > >> Best, Michael > >> > >> On Tue, May 22, 2012 at 11:40 AM, Robbie Edwards > >> <robbie.edwa...@gmail.com> wrote: > >> > Hi all, > >> > > >> > Thanks for the replies, but I realize I've done a bad job explaining > my > >> > problem. To help, I've created some sample data to explain the > problem. > >> > > >> > df <- data.frame(x=c(1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12), y=c(109, > >> > 232, > >> > 363, 496, 625, 744, 847, 928, 981, 1000, 979, 912), s=c(109, 341, 704, > >> > 1200, 1825, 2569, 3416, 4344, 5325, 6325, 7304, 8216)) > >> > > >> > In this data frame, y results from y = x * b1 + x^2 * b2 + x^3 * b3 > and > >> > s > >> > is sum of the current y and all previous y (s3 = y1 + y2 + y3). > >> > > >> > I know I can find b1, b2 and b3 using: > >> > lm(y ~ 0 + x + I(x^2) + I(x^3), data=df) > >> > > >> > yielding... > >> > Coefficients: > >> > x I(x^2) I(x^3) > >> > 100 10 -1 > >> > > >> > However, I need to find b1, b2 and b3 using the s column. The reason > >> > being, I don't actually know the values of y in the actual data set. > >> > And > >> > in the actual data, I only have a few of the values. Imagine this > data > >> > is > >> > being used a reward schedule for like a loyalty points program. y > >> > represents the number of points needed for each level while s is the > >> > total > >> > number of points to reach that level. In the real problem, my data > >> > looks > >> > more like this: > >> > > >> > d <- data.frame(x=c(1, 4, 9, 12), s=c(109, 1200, 5325, 8216)) > >> > > >> > Where I need to use a few sample points to help define the parameters > of > >> > the curve. > >> > > >> > thanks again and hopefully this makes the problem a bit clearer. > >> > > >> > robbie > >> > > >> > > >> > > >> > On Fri, May 18, 2012 at 7:40 PM, David Winsemius > >> > <dwinsem...@comcast.net>wrote: > >> > > >> >> > >> >> On May 18, 2012, at 1:44 PM, Robbie Edwards wrote: > >> >> > >> >> Hi all, > >> >>> > >> >>> I'm trying to model some data where the y is defined by > >> >>> > >> >>> y = summation[1 to 50] B1 * x + B2 * x^2 + B3 * x^3 > >> >>> > >> >>> Hopefully that reads clearly for email. > >> >>> > >> >>> > >> >> cumsum( rowSums( cbind(B1 * x, B2 * x^2, B3 * x^3))) > >> >> > >> >> > >> >> > >> >> Anyway, if it wasn't for the summation, I know I would do it like > this > >> >>> > >> >>> lm(y ~ x + x2 + x3) > >> >>> > >> >>> Where x2 and x3 are x^2 and x^3. > >> >>> > >> >>> However, since each value of x is related to the previous values of > x, > >> >>> I > >> >>> don't know how to do this. Any help is greatly appreciated. > >> >>> > >> >>> > >> >>> > >> >> > >> >> David Winsemius, MD > >> >> West Hartford, CT > >> >> > >> >> > >> > > >> > [[alternative HTML version deleted]] > >> > > >> > ______________________________________________ > >> > 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. > > > > > [[alternative HTML version deleted]] ______________________________________________ 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.
