How to run R Scripts with NodeJs Rest API

R-Script+NodeJs+RestApi

This guide will show you how to integrate RScript with NodeJs. Finally, you will be able to create a simple rest API with r-script data.

You can integrate R script with NodeJs with simple steps.

First of all, you have to install

1. NodeJs
2. R
3. R studio

1. Try this simple code in R Studio.

Open the file in R studio and press CTRL+ENTER in each line. Then you can see the result on the right side.

Run R script in RStudio

Horray…if you are just NodeJs developer, Now you know how to run an RScript.

2. Create Hello World Node API

Create a new folder. Then open it in a terminal then type following codes

npm init
npm install — save express
touch index.js

index.js

var express = require('express');
var app = express(); 
app.get('/', function (req, res) {   
   res.send('Hello World');
}) 

var server = app.listen(8081, function () {   
   var port = server.address().port   
   console.log(`Example app listening at http://localhost:${port}`)
})

in the terminal run `node index.js` then go to http://localhost:8081/

Horray…if you are just R Dev, Now you know how to run a NodeJs app with Rest API.

3. Now run R scripts in Node

If you go to this page, you can see 2 options. 1 — Async and 2 — sync. I don’t recommend to use sync functions because it blocks the NodeJs app. So no need to learn bad things. Let's try Asynchronous way to run R Script in NodeJs.

I am going to use the same example in this page https://www.npmjs.com/package/r-script with some changes.

npm install r-script --save
create ex-async.R
create index.js

Use the this code and run npm start or node index.js . Then Go to — http://localhost:8081/ex-async .Probably you will get an error message 😈

4. Did you get an error with 👆? that means the repo owner has not fixed a bug. But you can fix it.

If you get this error, you can fix it. https://github.com/joshkatz/r-script/issues/27

TypeError: Cannot read property 'data' of undefined
    at executeExAsync (/Users/Admin/Desktop/r-node-example/index.js:13:17)
    at /Users/Admin/Desktop/r-node-example/index.js:29:2
    at Layer.handle [as handle_request] (/Users/Admin/Desktop/r-node-example/node_modules/express/lib/router/layer.js:95:5)
    at next (/Users/Admin/Desktop/r-node-example/node_modules/express/lib/router/route.js:137:13)
    at Route.dispatch (/Users/Admin/Desktop/r-node-example/node_modules/express/lib/router/route.js:112:3)
    at Layer.handle [as handle_request] (/Users/Admin/Desktop/r-node-example/node_modules/express/lib/router/layer.js:95:5)
    at /Users/Admin/Desktop/r-node-example/node_modules/express/lib/router/index.js:281:22
    at Function.process_params (/Users/Admin/Desktop/r-node-example/node_modules/express/lib/router/index.js:335:12)
    at next (/Users/Admin/Desktop/r-node-example/node_modules/express/lib/router/index.js:275:10)
    at expressInit (/Users/Admin/Desktop/r-node-example/node_modules/express/lib/middleware/init.js:40:5)

The issue with the r-script library. That means you have to change the r-script library. Go to r-script library in node_modules folder then go to index.js. You can find the following code.

function init(path) {
   var obj = new R(path);
   return _.bindAll(obj, "data", "call", "callSync");
}

Change it to

function init(path) {
  var obj = new R(path);
  _.bindAll(obj, "data", "call", "callSync");
  return obj;
}

Then your code will work but it is not the correct way to do it. All you have to do is move r-script folder to the working folder and do that change.

You also have to change the import statement, remove `r-script` from package.json, etc. To minimize that, I published this source code to a git repo. You can download and try.

https://github.com/deshanm/r-node-example

For your information

• Limitation => You cannot pass a lot of data from NodeJs to RScript because of OS limitation.
• You can find answers for some issues in the git repo https://github.com/joshkatz/r-script/issues