Plot R graph Dynamically from JSP using JRI

Question

I was using R to plot the graph using JRI. I used the below code:

Rengine re = new Rengine (new String [] {"--vanilla"}, false, null);
re.eval("jpeg('<filename>')";
re.eval("plot(x,y)");
re.eval("dev.off()");

And calling the generated file from the jsp using

 <\img src='<filename>'/>

Instead of saving and calling the file in "img" tag, is it possible to plot the graph dynamically? I want to display the graph in the browser. Please suggest.

hrbrmstr · Accepted Answer · 2015-08-18 12:12:31Z

1

You can use data URIs and inline the graphics:

library(base64enc)

# unique filename; you can specify tmpdir for the 
# location where the png will be written
this_file <- tempfile("supercoolplot", fileext=".png")

# make a png
png(file=this_file <- tempfile("supercoolplot", fileext=".png"), width=200, height=200, bg="transparent")
plot(sample(1:10, 10, replace=TRUE)) # randomize plot
rect(1,5,3,7,col="white")
dev.off()

# show you the file
print(this_file)

# encode the png
encoded_png <- sprintf("<img src='data:image/png;base64,%s'/>", base64encode(this_file))

# optionally remove the offending file
# if you use the tmpdir option then you can prbly leave the
# file there and serve it up via the <img/> tag directly
# vs encode it below
unlink(this_file)

# see what we did (only showing part of the string)
substr(encoded_png, 1, 80)

## [1] "<img src='data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAMgAAADICAYAAACtWK6eAAAD"

# prove it works (run this in your R Console / RStudio
htmltools::html_print(htmltools::HTML(encoded_png))

As noted, you can output the png (or jpeg in your case) to a tempfile/dir and (optionally) remove that when done.

edited Aug 18, 2015 at 12:12

answered Aug 18, 2015 at 10:58

hrbrmstr

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3 Comments

Ashish Anand Over a year ago

Thanks, I am able to generate the graph in the browser. My main concern was, since its an JSP, what if 100 users are using the JSP, then the value for x and y will change(based on users). So, if I am saving the plot in a file (myplot.png), it will get overwritten by other user's data. So, I was looking for a way not to save in a file and pull data, instead just display in a browser on the fly.

Ashish Anand Over a year ago

Thanks. Is it possible to open it in the same tab, it opens in a new tab.

hrbrmstr Over a year ago

You probably don't want to use htmltools::html_print(htmltools::HTML(encoded_png)) in your code. You just want the <img…/> string printed since it's JSP.

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