MSS - 2 months ago 7

R Question

I have two 3D plots, one was made using fitted values using library

`p3d`

`predict`

`interp`

`akima`

`persp`

I would like to know why the graph showing fitted values has a curve and the other one with predicted values doesn't have it.

First graph code:

`library(p3d)`

Init3d(family="serif", cex = 1)

Plot3d( TCL ~ reLDM+yr, nest6)

Axes3d()

fit = lm( TCL ~ reLDM+yr+I(yr^2)+I(reLDM*yr)+I(reLDM*yr^2), nest6)

Fit3d( fit )

Second graph code:

`library(akima)`

x <- nest6$reLDM

y <- nest6$yr

y2 <- y^2

z <- nest6$TCL

m <- lm(z ~ x*y+y2+x:y2)

i <- 25

xtemp <- seq(min(x),max(x),length.out=i)

xrange <- rep(xtemp,times=i)

ytemp <- seq(min(y),max(y),length.out=i)

yrange <- rep(ytemp,each=i)

y2temp <- seq(min(y2),max(y2),length.out=i)

y2range <- rep(y2temp,each=i)

newdata <- data.frame(x=xrange,y=yrange,y2=y2range)

zhat <- predict(m,newdata=newdata)

xyz <- interp(xrange,yrange,zhat)

jet.colors <- colorRampPalette( c("yellow", "red", "blue") )

nbcol <- 500

color <- jet.colors(nbcol)

nrz <- length(xyz[[1]])

ncz <- length(xyz[[2]])

z<-xyz[[3]]

zfacet <- z[-1, -1] + z[-1, -ncz] + z[-nrz, -1] + z[-nrz, -ncz]

facetcol <- cut(zfacet, nbcol)

quartz()

persp(xyz,xlab="x",ylab="y",zlab="z", cex.lab = 1,cex.axis = 1,

theta = 35, phi = 50,col=color[facetcol], border="grey40", ticktype = "detailed", zlim=c(1,7))

You will find the dataset in this link, it big so it was not possible to post it here: https://www.dropbox.com/s/czdascoq02alm46/TCL16_26.csv?dl=0

My model was done using lm(), I read in a post that there is no difference between fitted and predict functions in a simple linear regression model. However, in akima I am using the interp command wich I understand it estimates values between two known data points (basically fills the missing data gaps).

Another difference I found is that predicted values plot uses new data from the maximum and minimum range of values in the original data set. For fitted values there is one value per observation.

I have problems explaining this to my supervisor, he thinks it is not enough reason. What would be a better explanation why is the curve missing in the second graph?

Answer

Source (Stackoverflow)

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