Apologies for the re-post; the earlier time I'd posted I did not have all the details.

My colleague, who quit the firm was a C# programmer, was forced to write Java code that involved (large, dense) matrix multiplication.

He's coded his own DataTable class in Java, in order to be able to

a) create indexes to sort and join with other DataTables

b) do matrix multiplication.

The code in its current form is NOT maintainable/extensible. I want to clean up the code, and thought using something like R within Java will help me focus on business logic rather than sorting, joining, matrix multiplication, etc.

Plus, I'm very new to the concept of DataTable; I just want to replace the DataTable with 2D arrays, and let R handle the rest.

(I currently do not know how to join 2 large datasets in java very efficiently

Please let me know what you think. Also, are there any simple examples that I can take a look at?