Papers that use R vs Stata Is there any way to tell if a paper used R instead of Stata or Matlab for the estimation? I know it doesn't matter for the quality of the paper, but I'd just be interested to see how many papers use one software over the other. 

I'm thinking an easy way might be by looking at the figures- ggplot means R, for example. 

Again, not really an economics question, but it's about economics papers.
The main economic journals are slowly starting to require authors to make their data and the code of their analysis available as part of the online appendix. When this is the case, it is easy to figure out which software was used.

One example are recent publications in the American Economic Review. For instance,


Calsamiglia, Caterina, Guillaume Haeringer, and Flip Klijn. 2010. "Constrained School Choice: An Experimental Study." American Economic Review, 100(4): 1860-74. https://www.aeaweb.org/articles.php?doi=10.1257/aer.100.4.1860


the online appendix of which contains the complete STATA code of the statistical analysis.

If the code is not available at the journal's webpage, other alternatives involve :


Checking the website of the authors. 
Contacting the authors themselves to ask if they could send you their code.


None of these methods are great if you're trying to gather a sizable or representative dataset of software used in econ papers, but for anecdotal data, they should do the trick.