Using R in PostgreSQL
Instructions on Use
To use R from pgAdmin III, follow the instructions in this tutorial: choose the database, click SQL, and run "CREATE EXTENSION plr;". This allows R functions to be used in this database from then on. You should be able to run the given examples in the tutorial after this is done. This was run on databases tigertest and template1.
Another possibly useful presentation on PL/R.
How PL/R was installed
On 2018-01-18, PL/R was installed to allow PostgreSQL users to use R functions from SQL queries. It was installed using this tutorial. The link from the tutorial for PL/R doesn't work, I used this instead.
It required R version 3.3.0 for PL/R to work with PostgreSQL 9.5. If the environmental variables R_HOME or PATH are edited so that they point to a different version of R, this might not work, and PL/R might have to be reinstalled. If the version of PostgreSQL is updated, both the R version and PL/R version will have to match it as well.