The R programming language is primarily designed for statistical computing and mostly used by researchers without a background in computer science. R provides a wide range of dynamic features and peculiarities that are difficult to analyze statically like dynamic scoping and lazy evaluation with dynamic side effects. At the same time, the R ecosystem lacks sophisticated analysis tools that support researchers in understanding and improving their code. In this paper, we present a novel static dataflow analysis framework for the R programming language that is capable of handling the dynamic nature of R programs and produces the dataflow graph of given R programs. This graph can be essential in a range of analyses, including program slicing, which we implement as a proof of concept. The core analysis works as a stateful fold over a normalized version of the abstract syntax tree of the R program, which tracks (re-)definitions, values, function calls, side effects, external files, and a dynamic control flow to produce one dataflow graph per program. We evaluate the correctness of our analysis using output equivalence testing on a manually curated dataset of 779 sensible slicing points from executable real-world R scripts. Additionally, we use a set of systematic test cases based on the capabilities of the R language and the implementation of the R interpreter and measure the runtimes well as the memory consumption on a set of 4,230 real-world R scripts and 20,815 packages available on R’s package manager CRAN. Furthermore, we evaluate the recall of our program slicer, its accuracy using shrinking, and its improvement over the state of the art. We correctly analyze almost all programs in our equivalence test suite, preserving the identical output for 99.7 % of the manually curated slicing points. On average, we require 576 ms to analyze the dataflow and around 213 kB to store the graph of a research script. This shows that our analysis is capable of analyzing real-world sources quickly and correctly. Our slicer achieves an average reduction of 84.8 % of tokens indicating its potential to improve program comprehension.

Context Comprehending code is crucial in all areas of software development, with many existing supporting tools and techniques for various languages. However, for R, a widely used programming language, especially in the field of statistical computing, the support is limited. R offers a large number of packages as well as dynamic features, which make it challenging to analyze and understand. Objective We aim to (i) gain a better understanding of how R is used in the real world, (ii) devise better analysis strategies for R, which are able to handle its dynamic nature, and (iii) improve the comprehension of R scripts by using these analyses, providing new methods and procedures applicable to program comprehension in general. Method In eight contributions, we analyze feature usage in R scripts, develop a new static dataflow analysis intertwining control and dataflow, and more. We enable and propose new techniques for program comprehension using a combination of static and dynamic analysis.

Context Many researchers rely on the R programming language to perform their statistical analyses and visualizations in the form of R scripts. However, recent research and experience show, that many of these scripts contain problems. From being hard to comprehend by combining several analyses and plots into a single source file to being non-reproducible, with a lack of analysis tools supporting the writing of correct and maintainable code. Objective In this work, we address the problem of comprehending and maintaining R scripts by proposing flowR, a program slicer and static dataflow analyzer for the R programming language, which can be integrated directly into Visual Studio Code. Given a set of variables of interest, like the generation of a single figure in a script, flowR automatically reduces the program to the parts relevant for the output of interest, like the value of a variable. Method First, we use static program analysis to construct a detailed dataflow graph of the R script. The analysis supports loops, function calls, side effects, sourcing external files, and even redefinitions of R's primitive constructs. Subsequently, we calculate the program slice by solving a reachability problem on the graph, collecting all required parts and presenting them to the user. Results Providing several interactive ways of slicing the program, we require an average of 16 ms to calculate the slice on a given dataflow graph, reducing the code by around 94% of tokens.

Context The R programming language has a huge and active community, especially in the area of statistical computing. Its interpreted nature allows for several interesting constructs, like the manipulation of functions at run-time, that hinder the static analysis of R programs. At the same time, there is a lack of existing research regarding how these features, or even the R language as a whole are used in practice. Objective In this paper, we conduct a large-scale, static analysis of more than 50 million lines of real-world R programs and packages to identify their characteristics and the features that are actually used. Moreover, we compare the similarities and differences between the scripts of R users and the implementations of package authors. We provide insights for static analysis tools like the lintr package as well as potential interpreter optimizations and uncover areas for future research. Method We analyze 4 230 R scripts submitted alongside publications and the sources of 19 450 CRAN packages for over 350 000 R files, collecting and summarizing quantitative information for features of interest. Results We find a high frequency of name-based indexing operations, assignments, and loops, but a low frequency for most of R's reflective functions. Furthermore, we find neither testing functions nor many calls to R's foreign function interface (FFI) in the publication submissions. Conclusion R scripts and package sources differ, for example, in their size, the way they include other packages, and their usage of R's reflective capabilities. We provide features that are used frequently and should be prioritized by static analysis tools, like operator assignments, function calls, and certain reflective functions like load.