From: Roger Bivand <Roger.Bivand_at_nhh.no>

Date: Tue 14 Feb 2006 - 19:24:06 EST

Date: Tue 14 Feb 2006 - 19:24:06 EST

On Mon, 13 Feb 2006, Denis Chabot wrote:

*> Hi,
**>
*

> This is probably documented, but I cannot find the right words or

*> expression for a search. My attempts failed.
**>
**> I have a data frame of 3 vectors (x, y and z) and would like to
**> transform this so that I could use persp. Presently I have y-level
**> copies of each x level, and a z value for each x-y pair. I need 2
**> columns giving the possible levels of x and y, and then a
**> transformation of z from a long vector into a matrix of x-level rows
**> and y-level columns. How do I accomplish this?
*

Well, image() and friends have a rather strange representation, so it isn't obvious (see the help page:

"Notice that 'image' interprets the 'z' matrix as a table of 'f(x[i], y[j])' values, so that the x axis corresponds to row number and the y axis to column number, with column 1 at the bottom, i.e. a 90 degree counter-clockwise rotation of the conventional printed layout of a matrix.").

So:

Depth <- seq(40,220, 20)

Temp <- seq(-1, 6, 0.5)

My.data <- expand.grid(Depth=Depth, Temp=Temp)
predgam <- -0.5*My.data$Depth + 12.5*My.data$Temp + 8*rnorm(nrow(My.data))
pred.data <- data.frame(My.data, predgam)
library(lattice)

levelplot(predgam ~ Depth + Temp, pred.data) # for sanity check
z <- t(matrix(predgam, nrow=length(Temp), byrow=TRUE)) # see "Notice"
image(Depth, Temp, z)

persp(Depth, Temp, z)

should do it, since the data are already in a regular grid.

*>
*

> In this example, I made a set of x and y values to get predictions

*> from a GAM, then combined them with the predictions into a data
**> frame. This is the one I'd like to transform as described above:
**>
**> My.data <- expand.grid(Depth=seq(40,220, 20), Temp=seq(-1, 6, 0.5))
**> predgam <- predict.gam(dxt.gam, My.data, type="response")
**> pred.data <- data.frame(My.data, predgam)
**>
**> pred.data has 150 lines and 3 columns.
**>
**> Thanks for your help,
**>
**> Denis Chabot
**>
**> ______________________________________________
**> R-help@stat.math.ethz.ch mailing list
**> https://stat.ethz.ch/mailman/listinfo/r-help
**> PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html
**>
*

-- Roger Bivand Economic Geography Section, Department of Economics, Norwegian School of Economics and Business Administration, Helleveien 30, N-5045 Bergen, Norway. voice: +47 55 95 93 55; fax +47 55 95 95 43 e-mail: Roger.Bivand@nhh.no ______________________________________________ R-help@stat.math.ethz.ch mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.htmlReceived on Tue Feb 14 19:28:41 2006

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