RCall graphics

Simon Byrne

16th April, 2015

These are some short notes on using R graphics through Julia using RCall



In [1]:

    
using RCall

Writing to a file

The standard R method, via opening a device, plotting, and closing it, works as it does in R.



In [2]:

    
reval("pdf('/tmp/aa.pdf')"); # opens new device
reval("plot(1:10)"); # create plot
reval("dev.off()"); # close device (writes to file)
isfile("/tmp/aa.pdf")









    Out[2]:





true

If doing this from within IJulia (see below), you should create and close the device within the one cell.

IJulia

From within the IJulia notebook interface, standard R plotting routines can be called directly, and the resulting graphics output (if any) will be displayed after evaluation, but before any printed values.



In [3]:

    
rprint("plot(1:10)")

The NULL here is the return value of the plot function. As in R, the graphics are side effects, and not directly representable by values.

Technical details

The implementation is fairly simple:

Before the cell is evaluated, a new graphics device is created (currently either png(...) or svg(...)).
After the cell has been evaluated, the device is closed (through dev.off()), and displayed.

The graphics device is controlled by the RCall.ijulia_setdevice function:

The first argument should be a MIME object. Currently supported are:
- MIME("image/png") [default]
- MIME("image/svg+xml")
Any extra arguments are passed to the relevant graphics device.



In [4]:

    
RCall.ijulia_setdevice(MIME("image/svg+xml")) # use SVG device



In [5]:

    
rprint("library(ggplot2)")









    



[1] "ggplot2"   "stats"     "graphics"  "grDevices" "utils"     "datasets" 
[7] "methods"   "base"



In [6]:

    
rprint("ggplot(mtcars, aes(wt, mpg)) + geom_point()")



In [7]:

    
RCall.ijulia_setdevice(MIME("image/png"),width=480,height=400) # use PNG device, options passed as keywords

Plotting Julia objects

Any Julia objects that can be converted to R objects via sexp can be passed via rcall:



In [8]:

    
X = linspace(0,pi,10)
rprint(rcall(:plot,X,sin(X)))

The crazy axis labels are due to R's non-standard evaluation. Unfortunately, Julia is very much standard in its evaluation, so you have to specify your own axis labels:



In [9]:

    
rprint(rcall(:plot,X,sin(X),xlab="x",ylab="sin(x)"))

Window display (experimental)

In a non-IJulia interactive session, by R will by default open a new window to display the plot. In order to enable interactive features, such as plot-resizing, you should start the R event loop via

RCall.rgui_start()

This runs frequent calls to R to check if the plot has changed, and redraw if necessary. It can be stopped with

RCall.rgui_stop()