# Combining ggplot Images

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The ggplot2 package provides an excellent platform for data visualization. One (minor) drawback of this package is that combining ggplot images into one plot, like the par() function does for regular plots, is not a straightforward procedure. Fortunately, R user Stephen Turner has kindly provided a function called “arrange” that does exactly this. The function, taken from his blog, and an example of how it can be used is provided below.

vp.layout <- function(x, y) viewport(layout.pos.row=x, layout.pos.col=y) arrange <- function(..., nrow=NULL, ncol=NULL, as.table=FALSE) { dots <- list(...) n <- length(dots) if(is.null(nrow) & is.null(ncol)) { nrow = floor(n/2) ; ncol = ceiling(n/nrow)} if(is.null(nrow)) { nrow = ceiling(n/ncol)} if(is.null(ncol)) { ncol = ceiling(n/nrow)} ## NOTE see n2mfrow in grDevices for possible alternative grid.newpage() pushViewport(viewport(layout=grid.layout(nrow,ncol) ) ) ii.p <- 1 for(ii.row in seq(1, nrow)){ ii.table.row <- ii.row if(as.table) {ii.table.row <- nrow - ii.table.row + 1} for(ii.col in seq(1, ncol)){ ii.table <- ii.p if(ii.p > n) break print(dots[[ii.table]], vp=vp.layout(ii.table.row, ii.col)) ii.p <- ii.p + 1 } } } library(ggplot2) ; library(grid) p1 <- qplot(wt, mpg, data=mtcars) p2 <- ggplot(diamonds, aes(price, colour = cut)) + geom_density() arrange(p1,p2)

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