R/multiplot.R

In cboettig/cboettigR: A collection of useful functions and utilities I commonly use

#' Multiple plot function
#'
#' @param ... ggplot objects (as a list of ggplot objects)
#' @param plotlist alternate input of a list of ggplot objects 
#' @param file (argument not used currently)
#' @param cols Number of columns in layout 
#' @param layout A matrix specifying the layout. If present, 'cols' is ignored.
#' @author Winston Chang <winston@@stdout.org>
#' @details  
#' 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.
#' 
#' Adapted from:
#' http://www.cookbook-r.com/Graphs/Multiple_graphs_on_one_page_(ggplot2)
#' @return the plot object
#' @import grid ggplot2
#' @export
#' @examples 
#' library(ggplot2)
#' 
#' # This example uses the ChickWeight dataset, which comes with ggplot2
#' # First plot
#' p1 <- 
#'     ggplot(ChickWeight, aes(x=Time, y=weight, colour=Diet, group=Chick)) +
#'     geom_line() +
#'     ggtitle("Growth curve for individual chicks")
#' 
#' # Second plot
#' p2 <- 
#'     ggplot(ChickWeight, aes(x=Time, y=weight, colour=Diet)) +
#'     geom_point(alpha=.3) +
#'     geom_smooth(alpha=.2, size=1) +
#'     ggtitle("Fitted growth curve per diet")
#' 
#' # Third plot
#' p3 <- 
#'     ggplot(subset(ChickWeight, Time==21), aes(x=weight, colour=Diet)) +
#'     geom_density() +
#'     ggtitle("Final weight, by diet")
#' 
#' # Fourth plot
#' p4 <- 
#'     ggplot(subset(ChickWeight, Time==21), aes(x=weight, fill=Diet)) +
#'     geom_histogram(colour="black", binwidth=50) +
#'     facet_grid(Diet ~ .) +
#'     ggtitle("Final weight, by diet") +
#'     theme(legend.position="none")
#' 
multiplot <- function(..., plotlist=NULL, file, cols=1, layout=NULL) {
  # 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))
    }
  }
}