1. You should regress Elevation on Volume, no? 2. You are calling lm incorrectly for prediction. Please read ?lm and related links carefully and/or consult a tutorial. R-Help is really not the first place you should look for this sort of detailed info.
3. I think this is what you want: lm1 <- lm(Elevation ~ Vol, data = x6) ## assuming (1) above is correct d <- data.frame(Vol = 3000) ## assuming (1) above is correct predict(lm1, newdata = d) Cheers, Bert On Sat, Dec 9, 2023 at 10:50 AM javad bayat <j.bayat...@gmail.com> wrote: > Dear all; > > I have a dataframe with several columns. The columns are the elevation, > volume and the area of the cells (which were placed inside a polygon). I > have extracted them from DEM raster to calculate the volume under polygon > and the elevation for a specific volume of the reservoir. > > > head(x6,2) > Elevation Vol Area V_sum A_sum > 1 2145 13990.38 85.83053 13990.38 85.83053 > 2 2147 43129.18 267.88312 57119.56 353.71365 > > > tail(x6,2) > Elevation Vol Area V_sum A_sum > 158 2307 233.0276 233.02756 1771806968 15172603 > 159 2308 0.0000 71.65642 1771806968 15172674 > > I used a linear model to estimate the elevation for a specific volume, but > the codes do not work properly. > > lm1 = lm(x6[,1]~x6[,4]) > new_volume <- 3,000,000,000 > pred_elev <- predict(lm1, newdata = data.frame(volume = new_volume)) > pred_elev > > The results just estimated for the 159 rows of the dataframe, not the new > volume. > > > tail(pred_elev) > 154 155 156 157 158 159 > 2254.296 2254.296 2254.296 2254.296 2254.296 2254.296 > > Also I have used the approx function, but it does not work for the new > volume, too. > > > a = x6[,1] > > b = x6[,4] > > estimate <- 3,000,000,000 > > appro <- approx(b,a, xout = estimate) > > appro > $x > [1] 3e+09 > > $y > [1] NA > > I do not know why it has happened. > > Is there any way to do this? > Or maybe there is another way to do that. > I would be more than happy if anyone help me. > > Sincerely > > [[alternative HTML version deleted]] > > ______________________________________________ > R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see > 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 -- To UNSUBSCRIBE and more, see 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.
