Integrating PHP and R

August 18, 2010

(This article was first published on stotastic » R, and kindly contributed to R-bloggers)

“How can I integrate PHP and R?”

I know I’m not the only one who’s asked this question. After all, with great content management systems like Drupal, it would very cool to be able to drop an R module into some PHP code and instantly have a web app popping out some snazzy looking ggplot graphics. After spending some time Google searching for an easy implementation and finding very little in the PHP + R space, I was able to piece together a method for integrating the two. It uses no JavaScript… no AJAX… just plain old PHP.

The poor man’s R web app

Disclaimer: There are many reasons why you shouldn’t actually stick the following code on the web for all to see. It is a very stripped down example, which is great for experimenting on a localhost, but has some serious security flaws.

This implementation of PHP and R consists of only two files. One written in PHP, and the other an R script. The PHP returns a form which uses the GET method to send a variable N to the server. When the form is submitted, the PHP will then execute an R script from the shell using a combination of the PHP command exec() and the Rscript shell command. This command will pass the variable N to the R script. The R script will then execute and save a histogram plot of N normally distributed values to the filesystem. Finally, when the R script is complete, the PHP will return the HTML tag containing the saved images path. First, the PHP file…

<?php
// poorman.php
 
echo "<form action='poorman.php' method='get'>";
echo "Number values to generate: <input type='text' name='N' />";
echo "<input type='submit' />";
echo "</form>";
 
if(isset($_GET['N']))
{
  $N = $_GET['N'];
 
  // execute R script from shell
  // this will save a plot at temp.png to the filesystem
  exec("Rscript my_rscript.R $N");
 
  // return image tag
  $nocache = rand();
  echo("<img src='temp.png?$nocache' />");
}
?>

and the R script…

# my_rscript.R
 
args <- commandArgs(TRUE)
 
N <- args[1]
x <- rnorm(N,0,1)
 
png(filename="temp.png", width=500, height=500)
hist(x, col="lightblue")
dev.off()

Finally, to help you visualize the whole process a bit better, below is a screenshot of the results…

Some Issues

This is a very simple example that works fine on a localhost, but there are some BIG issues that need to be resolved before this code is opened up to the web.