R/cor.demo.R

In profpetrie/regclass: Tools for an Introductory Class in Regression and Modeling

cor.demo <-
function() {
    par(mfrow=c(1,1))
    plot(0,0,xlim=c(0,1),col="white",ylim=c(0,1),xlab="x",ylab="y",main="click plot to add points then click END below to stop demo",cex.main=0.9)
    rect(-1,.9,.2,2,col="white");  text(0.1,0.95,"r2 =    ")
    rect(0.55,.9,2,2,col="white");  text(0.8,0.95,"r2 (without red dot) =    ")
    
    rect(0,0,.1,.05,col="red");  text(0.05,.025,"END",cex=0.8)
    x <- c(); y <- c()
    r.old <- 0
    keep.going <- 1
    while (keep.going==1) {
        new.point <- unlist(locator(1))
        if( new.point[1] > .1 | new.point[2] > .05 ) {
            points(x,y,pch=20,cex=2,col="black")
            points(new.point[1],new.point[2],pch=20,cex=2,col="red")
            x <- c(x,new.point[1]);  y <- c(y,new.point[2])
            r <- round(cor(x,y),digits=2)
            rect(-1,.9,.2,2,col="white")
            text(0.075,1,paste("r =",r))
            text(0.075,0.95,paste("r2 =",r^2))
            if(length(x)>2) {
                rect(0.55,.9,2,2,col="white");
                text(0.8,1,paste("r (without red dot) =",round(r.old,digits=2)))
                text(0.8,0.95,paste("r2 (without red dot) =",round(r.old^2,digits=2))) }
            r.old <- r
        } else { keep.going <- 0 }
    }
}