#title multiplot.R

http://www.cookbook-r.com/Graphs/Multiple_graphs_on_one_page_(ggplot2)/
{{{
# Multiple plot function
#
# ggplot objects can be passed in ..., or to plotlist (as a list of ggplot objects)
# - cols:   Number of columns in layout
# - layout: A matrix specifying the layout. If present, 'cols' is ignored.
#
# If the layout is something like matrix(c(1,2,3,3), nrow=2, byrow=TRUE),
# then plot 1 will go in the upper left, 2 will go in the upper right, and
# 3 will go all the way across the bottom.
#
multiplot <- function(..., plotlist=NULL, file, cols=1, layout=NULL) {
  require(grid)

  # Make a list from the ... arguments and plotlist
  plots <- c(list(...), plotlist)

  numPlots = length(plots)

  # If layout is NULL, then use 'cols' to determine layout
  if (is.null(layout)) {
    # Make the panel
    # ncol: Number of columns of plots
    # nrow: Number of rows needed, calculated from # of cols
    layout <- matrix(seq(1, cols * ceiling(numPlots/cols)),
                    ncol = cols, nrow = ceiling(numPlots/cols))
  }

 if (numPlots==1) {
    print(plots[[1]])

  } else {
    # Set up the page
    grid.newpage()
    pushViewport(viewport(layout = grid.layout(nrow(layout), ncol(layout))))

    # Make each plot, in the correct location
    for (i in 1:numPlots) {
      # Get the i,j matrix positions of the regions that contain this subplot
      matchidx <- as.data.frame(which(layout == i, arr.ind = TRUE))

      print(plots[[i]], vp = viewport(layout.pos.row = matchidx$row,
                                      layout.pos.col = matchidx$col))
    }
  }
}
}}}

example
{{{
p <- ggplot(df99, aes(x=arrived_time, fill=구매여부))
p1 <- p + 
    geom_histogram(binwidth=5) + xlab("x") + ylab("y") +
    geom_vline(xintercept = median(x1), colour="red", linetype = "longdash") + 
    geom_vline(xintercept = median(x2), colour="black", linetype = "longdash") +
    geom_text(data = NULL, x = 50, y = 81, label = median(x2)) + 
    geom_text(data = NULL, x = 95, y = 81, label = median(x1))

label <- paste0("구매=", round(length(x1) / nrow(df99) * 100, 2), "%, 비구매=", round(length(x2) / nrow(df99) * 100, 2), "%")
p2 <- ggplot(df99, aes(x=factor(1), fill=구매여부)) + 
    geom_bar(width=1) + coord_polar(theta = "y") +
    geom_text(data = NULL, x = 1, y = 1, label = label) +
    xlab("") + ylab("")

multiplot(p1, p2, cols=2)
}}}