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From |
Stas Kolenikov <[email protected]> |

To |
[email protected] |

Subject |
Re: st: What is good programming practice in Stata? |

Date |
Thu, 19 Nov 2009 10:25:25 -0600 |

2009/11/19 Joachim Landström <[email protected]>: > What is Good Stata Programming Practice? Since there's exactly one book on Stata programming (http://www.stata.com/bookstore/isp.html), I think we all should blame Kit Baum for failing to bring up perfect Stata code writing habits in this community! To Joachim's questions about classes and all -- off the top of my head, I can name two people who used Stata classes and OO features -- Vince Wiggins (and his team) who wrote Stata graphical engine, and Sergiy Radyakin (and his team) who wrote some crazy data management stuff at WorldBank. As Nick Cox said, most of statistical programming is really straightforward in terms of computer science concepts. The most complicated algorithms are loops (and R, for instance, still struggles to have efficient loops, by the way), and they mostly arise in (1) data structures that have some repetition, (2) iterative maximization (taken care of by Stata Corp with -ml- and -mata: optimize-), and (3) parameter estimates display. And then the most complicated data structures that are commonly used are panel data. There might be some sort of beneficial data structures to describe a neighborhood of an observation -- they would come extremely handy in non-parametric smoothing, spatial problems, multivariate clustering or matching estimators. In some of these areas, Stata does lag behind R (where, I believe, the brute force of sifting through the data set to find the neighbors is still used). Can these kind of data structure problems solved with objects? Are there special data structures invented for those purposes that could be coded in Stata? I don't really know, but I doubt there has been computer science research behind these topics. Relative simplicity of Stata programming means "everybody can cook", qutoing Auguste Gusteau from "Ratatouille" :)). Is this do-it-yourself openness of Stata a double-edged sword? It is easy to write your own programs, so is it too easy to write programs in bad style? Sometimes, looking at other people's Stata code, I have some mental comments like "This is easier achieved via local macro manipulation" or "If you really want this to work with the rest of Stata, you need to ereturn this properly" or "What the heck does this underscore command do?" (with Stata Corp. code -- it is usually transparent to read until you hit something undocumented "because we did not think anybody would be interested in knowing how it works"). Other times, I look at other people's code and think, "How come I don't know this command after 10+ years of Stata experience?" (the answer often is, it came out in the new release, and I did not bother to read -help whatsnew- carefully enough :)) or "Thank God they broke down this parsing problem into five lines". Well, if it were possible to have peer review of the code submitted to SSC or Stata Journal, just like there is peer review of research submitted to academic journals, we would have better code floating around; but there are simply no human resources to do that. I believe most people would stop at where the code produces apparently correct results for their own research problems most of the time (remember that Stata is the software for professionals who need to write research papers and/or project reports; they use it to solve their problems rather than develop some cute packages). In all likelihood, this code can be improved in terms of stability and usability. Some people are interested in producing re-usable code that would help others (altruism of this community is still a badly under-studied area; see however http://ideas.repec.org/p/boc/dcon09/6.html), and some people are better at programming because of their formal training or extensive earlier experience, so they produce better code. But requiring everybody to write code in perfect style is as unrealistic as asking everybody to exercise for a couple of hours every day -- yes, there are obvious benefits to both, but few people can really get to do that given that they have other things to accomplish. -- Stas Kolenikov, also found at http://stas.kolenikov.name Small print: I use this email account for mailing lists only. * * For searches and help try: * http://www.stata.com/help.cgi?search * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/

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