postgresql-12-plr binary package in Ubuntu Focal amd64

 R is a language and environment for statistical computing and graphics,
 providing a wide variety of statistical and graphical techniques (linear and
 nonlinear modelling, statistical tests, time series analysis, classification,
 clustering, and so on).
 .
 PostgreSQL is an open source SQL database server.
 .
 This package provides a procedural language interface to R from
 PostgreSQL. Procedural languages are used to write functions
 which can be called in database queries.

Source package