# [R] How can we let "multiplot.R" return a plot?

jpm miao miaojpm at gmail.com
Fri Jan 15 06:26:49 CET 2016

```Hi,

The function "ggplot" does plot and return a plot. For example, we can
write:

y = ggplot(.. .....)  Then y is  a plot.

How can we modify the multiplot function so that it can also return a
plot?  Multiplot.R is here:

http://www.cookbook-r.com/Graphs/Multiple_graphs_on_one_page_(ggplot2)/,
and the code is as below.

Any advice on returning a multi-ggplot would help!

Thanks,

Miao

# 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) { library(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[]) } 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)) } } }

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