Disordered vectors in R: introducing the disordR package

Objects in the {\tt stl map} class of {\tt C++} associate a value to each of a set of keys. Accessing values or keys of such an object is problematic in the R programming language because the value-key pairs are not stored in a well-defined order. This document motivates and discusses the concept of "disordered vector" as implemented by the {\tt disordR} package which facilitates the handling of {\tt map} objects. Values and keys of a map are stored in an implementation-specific way so certain extraction and replacement operations should be forbidden. For example, if values are real, then the "first" value is implementation specific\ldots but the maximum value has a well-defined result. The {\tt disordR} package makes forbidden operations impossible while allowing transparent R idiom for permitted operations. An illustrative R session is given in which the package is used abstractly, without reference to any particular application, and then shows how it can be used to manipulate multivariate polynomials. The {\tt disordR} package is a dependency of {\tt clifford}, {\tt freealg}, {\tt hyper2}, {\tt mvp}, {\tt spray}, {\tt stokes}, and {\tt weyl}. The {\tt disordR} package is available on CRAN at \url{https://CRAN.R-project.org/package=disordR}.