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

[David Winsemius]

> On Jan 14, 2016, at 9:26 PM, jpm miao <miaojpm at gmail.com> wrote:
> 
> 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[[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)) } } }
> 
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David Winsemius
Alameda, CA, USA