I see a many times in job description for data scientist asking for Python/Java experience and disregard R. Below is a personal email I received from chief data scientist of a company I applied for through linkedin.


  X, Thanks for connecting and expressing interest. You do have good
  Analytics Skills. However,  all our data scientists must have  good
  programming skills in Java/Python as we are a internet/mobile
  organisation and everything we do is online.


While I respect the decision of the chief data scientist, I am unable to get a clear picture as to what are the tasks that Python can do that R cannot do. Can anyone care to elaborate? I am actually keen to learn Python/Java, provided I get a bit more detail.

Edit: I found an interesting discussion on Quora.
Why is Python a language of choice for data scientists?

Edit2: Blog from Udacity on Languages and Libraries for Machine Learning

So you can integrate with the rest of the code base. It seems your company uses a mix of Java and python. What are you going to do if a little corner of the site needs machine learning; pass the data around with a database, or a cache, drop to R, and so on? Why not just do it all in the same language? It's faster, cleaner, and easier to maintain.

Know any online companies that run solely on R? Neither do I...

All that said Java is the last language I'd do data science in.
