plotmatrix with aesthetics

plotmatrix2.R

plotmatrix2 <- function (data, mapping = aes())
{
    grid <- expand.grid(x = 1:ncol(data), y = 1:ncol(data))
    grid <- subset(grid, x != y)
    all <- do.call("rbind", lapply(1:nrow(grid), function(i) {
        xcol <- grid[i, "x"]
        ycol <- grid[i, "y"]
        data.frame(xvar = names(data)[ycol], yvar = names(data)[xcol], 
            x = data[, xcol], y = data[, ycol], data)
    }))
    all$xvar <- factor(all$xvar, levels = names(data))
    all$yvar <- factor(all$yvar, levels = names(data))
    densities <- do.call("rbind", lapply(1:ncol(data), function(i) {
        data.frame(xvar = names(data)[i], yvar = names(data)[i], 
            x = data[, i])
    }))
    mapping <- defaults(mapping, aes_string(x = "x", y = "y"))
    class(mapping) <- "uneval"
    ggplot(all) + facet_grid(xvar ~ yvar, scales = "free") + 
        geom_point(mapping, na.rm = TRUE) + stat_density(aes(x = x, 
        y = ..scaled.. * diff(range(x)) + min(x)), data = densities, 
        position = "identity", colour = "grey20", geom = "line")
}

Where does the "defaults" function come from?

I found it in plyr. Sorry!