I am trying to do some analysis for multiple sites, in my example I am using only two, but the same will done on many sites. It's just ONE line, so I hope somebody can give a me a hand by email.
Look at the loop to make the plot x ~ y. If the curve function is removed from the loop everything works fine, but when I tried to add the curve to the plot, I get the following error:
Error in xy.coords(x, y) : x and y lengths differ In addition: Warning message: 'newdata' had 101 rows but variable(s) found have 6 rows
I know this error should be a hint about how to proceed but I am stuck figuring ways to make the curve to print in the plots.
Any hints on how to solve this issue would be greatly appreciated.
Sincerely,
Jose
PS.
> version
_
platform i386-pc-mingw32
arch i386
os mingw32
system i386, mingw32
status
major 2
minor 0.1
year 2004
month 11
day 15
language R###################################################################
# some data
site <- c(1,1,1,1,1,1,2,2,2,2,2,2)
nrate <- c(0,60,90,120,150,180,0,60,90,120,150,180)
yield <- c(161.7,187.1,188.5,196.6,196.0,196.5,160.7,186.1,189.5,194.6,195.0,198.5)
site <- as.factor(site)
# file name
fname <- levels(site)
i <- nchar(fname) == 1
fname[i] <- paste("0", fname[i], sep = "")
fname <- paste("site", fname, ".eps", sep = "")################################################################### ###################################################################
for (i in 1:length(levels(site))) {
j <- site == levels(site)[i]
x <- nrate[j]
y <- yield[j]
out <- try(lm(y ~ x + I(x^2)), silent = TRUE)
plot(y ~ x,
pch = 16,
xlab = expression(paste("Nitrogen rate [lbs ac" ^-1,"]")),
ylab = expression(paste("Corn yield [bu ac"^-1,"]")))
curve(predict(out, data.frame(nrate = x)), add = T)
title(paste("Site", i))
# dev.copy2eps(file = fname[i], horizontal = TRUE)
}
###################################################################
###################################################################-- Jose A. Hernandez Department of Soil, Water, and Climate University of Minnesota 1991 Upper Buford Circle St. Paul, MN 55108
Ph. (612) 625-0445, Fax. (612) 625-2208
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