Correlation Scatter-matrix plot with different point size (in R)

I just came a cross this nice code that makes this scatter matrix plot:

_{(source: free.fr)}

And wanted to implement it to a likret scale variables (integers of 1 to 5) by making the dot's sizes/colors (in the lower triangle) differ according to how many options of that type occurs (lik开发者_StackOverflow社区e the effect the jitter might have given me).

Any idea on how to do this on the base plotting mechanism ?

Update:

I made the following function, but don't know how to have the scale of the dots always be "good", what do you think ?

panel.smooth2 <- function (x, y, col = par("col"), bg = NA, pch = par("pch"), 
                    cex = 1, col.smooth = "red", span = 2/3, iter = 3, ...) 
{
    require(reshape)
    z <- merge(data.frame(x,y), melt(table(x ,y)),sort =F)$value
    z <- z/ (4*max(z)) 

    symbols( x, y,  circles = z,#rep(0.1, length(x)), #sample(1:2, length(x), replace = T) ,
            inches=F, bg="blue", fg = bg, add = T)

    # points(x, y, pch = pch, col = col, bg = bg, cex = cex)
    ok <- is.finite(x) & is.finite(y)
    if (any(ok)) 
        lines(stats::lowess(x[ok], y[ok], f = span, iter = iter), 
            col = col.smooth, ...)
}



a1 <- sample(1:5, 100, replace = T)
a2 <- sample(1:5, 100, replace = T)
a3 <- sample(1:5, 100, replace = T)
aa <- data.frame(a1,a2,a3)


pairs(aa , lower.panel=panel.smooth2)

You can use 'symbols' (analogous to the methods 'lines', 'abline' et al.)

This method will give you fine-grained control over both symbols size and color in a single line of code.

Using 'symbols' you can set the symbol size, color, and shape. Shape and size are set by passing in a vector for the size of each symbol and binding it to either 'circles', 'squares', 'rectangles', or 'stars', e.g., 'stars' = c(4, 3, 5, 1). Color is set with 'bg' and/or 'fg'.

symbols( x, y, circles = circle_radii, inches=1/3, bg="blue", fg=NULL) 

If i understand the second part of your question, you want to be reasonably sure that the function you use to scale the symbols in your plot does so in a meaningful way. The 'symbols' function scales (for instance) the radii of circles based on values in a 'z' variable (or data.frame column, etc.) In the line below, I set the max symbol size (radius) as 1/3 inches--every symbol except for the largest has a radius some fraction smaller, scaled by the ratio of the value of that dat point over the largest value. than that one in proportion to Is this a good choice? I don't know--it seems to me that diameter or particularly circumference might be better. In any event, that's a trivial change. In sum, 'symbols' with 'circles' passed in will scale the radii of the symbols in proportion to the 'z' coordinate--probably best suited for continuous variables. I would use color ('bg') for discrete variables/factors.

One way to use 'symbols' is to call your plot function and pass in type='n' which creates the plot object but suppresses drawing the symbols so that you can draw them with the 'symbols' function next.

I would not recommend 'cex' for this purpose. 'cex' is a scaling factor for both text size and symbols size, but which of those two plot elements it affects depends on when you pass it in--if you set it via 'par' then it acts on most of the text appearing on the plot; if you set it within the 'plot' function then it affects symbols size.

Sure, just use cex:

set.seed(42)
DF <- data.frame(x=1:10, y=rnorm(10)*10, z=runif(10)*3) 
with(DF, plot(x, y, cex=z))

which gives you varying circle sizes. Color can simply be a fourth dimension.