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Converting S-Plus Applications into R

Converting S-Plus Applications into R. Andy Nicholls (anicholls@mango-solutions.com). Context. Context. Mango are speaking with an increasing number of customers who would like to convert their existing S+ application into an R equivalent. Why Convert an S+ Application to R?.

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Converting S-Plus Applications into R

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  1. Converting S-Plus Applications into R Andy Nicholls (anicholls@mango-solutions.com)

  2. Context

  3. Context • Mango are speaking with an increasing number of customers who would like to convert their existing S+ application into an R equivalent

  4. Why Convert an S+ Application to R? We have seen three primary drivers for change: • Long term cost reduction (S+ licenses) • Incompatibility of S+ version with new OS • Withdrawal of Support • Wider uptake of R in industry Clearly R is a natural choice as a replacement for S+

  5. Aim • To provide a high level overview of the considerations for converting an S+ application to R

  6. Agenda • Context • Considerations • Menu System • Code Conversion • Validation and Testing

  7. Considerations

  8. This is Easy, Right? Some (true?) statements: • R can be considered as a different implementation of S • There are some important differences, but much code written for S runs unaltered under R Discuss... Source: www.r-project.org

  9. Considerations S+ applications can generally be split into two pieces: • An underlying library of code • A set of functions defining the menu system and help pages

  10. Case Study Multinational confectionary, food and drinks company • Existing S+ application consisting of an integrated menu and some analysis code • S+ libraries consisting of 7,000+ lines of S code spread over 80 functions • After removing those functions relating to the menu and help files, only around 3,000 lines of code remained

  11. Menu System

  12. S+ Menu System

  13. Menu System Opportunities • S+ Applications tend to be integrated into the S+ GUI • R systems can be also be integrated but require new code • The move to R represents an opportunity to hide the R GUI

  14. An Opportunity to Hide R

  15. An Opportunity to Hide R • Hiding R can improve user acceptance amongst non-technical colleagues • It can also improve the visual appeal of the system

  16. Menu Choices Some R/R-based technologies: • tcltk is R’s ‘recommended’ menu builder • Glade, RGtk2 • gWidgets • rpanel • Deducer • manipulate (Rstudio) • ...

  17. Menu Choices Other options: • Choice is almost limitless • Often they require a knowledge of other languages such as Java or C • Possibly warrants a standalone talk...

  18. Code Conversion

  19. Approach There are essentially two approaches to code conversion: • Direct Conversion • Test-based Conversion

  20. Direct Conversion • Requires knowledge of both languages (stdevvssd) • Relatively quick to achieve • Difficult to prove the new code does what the old code did

  21. Test-based Conversion • Generating unit tests in S+ requires some S+ knowledge • Takes some time to generate and document tests but better in the long-run • Unit tests give a definitive PASS/FAIL result • Can often be automated

  22. Code Conversion Challenges • The application upgrade usually coincides with an operating system upgrade • Windows (or other) version and R version need to be determined in advance • It is almost guaranteed that the new system will produce different results for the same test data!

  23. What is “different”? • Often this is simply rounding • Still require agreement on precision: 0.049782 vs 0.050436 • If simulation is involved this can be VERY difficult to define!!! • Appearance of graphics may also differ • Usually less of an issue

  24. Other Challenges As the business owner I want to use the opportunity to improve the application: • New menu items • New functionality • Modifications to existing functionality All of these require careful planning

  25. Validation and Testing

  26. Validation and Testing • This is not exciting! • When we use an application, we assume it has been “tested” and hope/require that it has been “validated” • But what does this really mean?

  27. Validation What is validation? • Design Qualification • Installation Qualification • Operational Qualification • Performance Qualification • A lengthy documentation exercise

  28. System Testing • Unit tests check individual pieces of code • A system is made up of many pieces • We need to ensure it has been pieced together correctly!

  29. System Testing Requires: • Patience • An independent tester/test team • Planning • More documentation!!!

  30. System Testing Recommended: • An automated build system • Hudson, Jenkins • Bug reporting system

  31. Summary • Converting an S+ application requires careful planning • It presents an opportunity to make improvements • Validation and independent testing are key to a successful migration

  32. Questions

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