new ggplot 2 syntax, return data object, print plot, fix wrong name for first argument

ggprplots.R

ggprplots <- function(fit, alpha=0.1) {
  design <- model.matrix(fit)
  
  # Skip the intercept term, if any.
  m0 <- if (colnames(design)[1] == '(Intercept)') { 2 } else { 1 }
  M <- ncol(design)

  data <- do.call(rbind, lapply(m0:M, function(m) {
    var <- colnames(design)[m]
    value <- design[,m]
    coef <- fit$coef[m]
    data.frame(var=var, value=value, coef=coef, residual=fit$residuals)
  }))
  
  p <- ggplot(data, aes(x=value, y=coef*value + residual))
  p <- p + facet_wrap(~ var, ncol=2, scale='free')
  p <- p + geom_point(alpha=alpha)
  p <- p + geom_smooth(method='lm', color='black', lty=2)
#  p <- p + geom_smooth(color='green')
  p <- p + labs(title="Component + Residual Plots")
  p <- p + theme_bw()
  print(p)
  invisible(data)
}