leverage.plots <<- function(model=NULL, X=NULL, y=NULL,
                            extra=.1,
                            cex=.5, cex.ident=.7, cex.axis=.8, cex.lab=.8,
                            win.ncol=5, frame.sz=3.0, ident=F, label.sel=NULL,...) {
  y.lab <- "Y"
  if(!is.null(model)) {
    X <- model.matrix(model)[,-1]  # assume intercept
    y <- model.frame(model)[,1]
    y.lab <- colnames(model.frame(model))[[1]]
  } else {
    if(is.null(X) | is.null(y))
      stop("function 'leverage.plots': if no model is given, give both X and y")
  }
  row.lab <- rownames(X)
  npred   <- ncol(X)
  win.ncol <- min(npred, win.ncol)
  win.nrow <- ceiling(npred/win.ncol)
  windows(width=frame.sz*(win.ncol), height=frame.sz*(win.nrow))
  par(mfrow=c(win.nrow,win.ncol), mgp=c(1.5,0.5,0), mar=c(3,3,1,1))
  for(i in 1:npred) {
    xi.adj <- resid(lm(X[,i] ~ X[,-i]))
    y.adj  <- resid(lm(y ~ X[,-i]))
    x.rg <- range(xi.adj);  xlim <- x.rg + c(-1,1)*diff(x.rg)*extra  
    y.rg <- range(y.adj);   ylim <- y.rg + c(-1,1)*diff(y.rg)*extra
    plot(x=xi.adj, y=y.adj, pch=16, xlim=xlim, ylim=ylim,
         xlab=paste(colnames(X)[i],"(adj)"), ylab=y.lab, cex=cex, ...)
    abline(lm(y.adj ~ xi.adj), col="gray70")
    if(!is.null(label.sel))
      text(x=xi.adj[label.sel], y=y.adj[label.sel], lab=row.lab[label.sel])
    if(i %in% ident) {
      cat("Identify by clicking near points; stop with R-click.\n")
      identify(x=xi.adj, y=y.adj, lab=row.lab, cex=cex.ident)
    }
  }
}
# Examples:
#   leverage.plots(lm(MEDV ~ ., data=boston))
#   leverage.plots(lm(MEDV ~ ., data=boston), ident=c(4,5))      # identify points for variables 4 and 5
#   leverage.plots(lm(MEDV ~ ., data=boston), label.sel=369:372) # label these cases 
# Instead of a model one can also give X and y arguments with model matrix X and response y.