From: Michael Rennie <mrennie_at_utm.utoronto.ca>

Date: Fri 26 Jan 2007 - 16:50:57 GMT

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 and provide commented, minimal, self-contained, reproducible code. Received on Sat Jan 27 03:56:05 2007

Date: Fri 26 Jan 2007 - 16:50:57 GMT

y1<-rnorm(40, 2) x1<-rep(1:2, each=20) x2<-rep(1:2, each=10 times=2)

ex.dat<-data.frame(cbind(y1,x1,x2))

ex.dat$x1<-factor(ex.dat$x1, labels=c("A", "B")) ex.dat$x2<-factor(ex.dat$x2, labels=c("C", "D"))

attach(ex.dat)

xbar<-tapply(ex.dat$y1, ex.dat[,-1], mean) xbar

#values I'd like to plot:

row.names(xbar) #levels of x1

xbar[,1] #mean response of y1 for group C (x2) across x1

#plot mean response y1 for group C against x1 (i.e., using x2 as a grouping

factor).

plot(row.names(xbar), xbar[,1], ylim=range[y1])

#This is where things break down. The error message states that I need

"finite xlim values" but I haven't assigned anything to xlim. If I just
plot the data:

plot(x1, y1)

stripchart(xbar[1,]~row.names(xbar), vert=T)

#However, I'd like to then add the values for the second set of means

(i.e., mean values for group D against x1, or (xbar[,2])) to the plot.

#I tried following up the previous command with:

points(row.names(xbar), xbar[,2])

#But that returns an error as well (NAs introduced by coercion).

Any suggestions?

Cheers,

Mike

PS- some of you might suggest for me to use interaction.plot, since this is essentially what I'm building here. True, but I can't get error bars using interaction.plot. I'm therefore trying to build my own version where I can specify the inclusion of error bars. Presumably the interaction.plot has figured out how to do what I'm attempting, so I have some faith that I am on the right track....

Michael Rennie

Ph.D. Candidate, University of Toronto at Mississauga
3359 Mississauga Rd. N.

Mississauga, ON L5L 1C6

Ph: 905-828-5452 Fax: 905-828-3792

www.utm.utoronto.ca/~w3rennie

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 and provide commented, minimal, self-contained, reproducible code. Received on Sat Jan 27 03:56:05 2007

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