Here are the steps for installing the required environment to run the OHDSI R packages. Four things needs to be installed:

1. R is a statistical computing environment. It comes with a basic user interface that is primarily a command-line interface.
2. RTools is a set of programs that is required on Windows to build R packages from source.
3. RStudio is an IDE (Integrated Development Environment) that makes R easier to use. It includes a code editor, debugging and visualization tools. Please use it to obtain a nice R experience.
4. Java is a computing environment that is needed to run some of the components in the OHDSI R packages, for example those needed to connect to a database.

# Instructions for Windows

In Windows, both R and Java come in 32-bit and 64-bits architectures. If you install R in both architectures, you must also install Java in both architectures. It is recommended to only install the 64-bit version of R.

## Installing R

2. After the download has completed, run the installer. Use the default options everywhere, with two exceptions: First, it is better not to install into program files. Instead, just make R a subfolder of your C drive as shown below. Second, to avoid problems due to differing architectures between R and Java, disable the 32-bit architecture as also shown below.

Once completed, you should be able to select R from your Start Menu.

## Installing RTools

3. Since R v4.0.0 you also need to add the following line to your .Renviron file, as described on the RTools page:

PATH="${RTOOLS40_HOME}\usr\bin;${PATH}"

## Installing Java

1. Go to https://java.com/en/download/manual.jsp, and select the Windows 64-bit installer as highlighted below. If you also installed the 32-bit version of R, you must also install the other (32-bit) version of Java.

# Verifying the installation

You should now be ready to go, but we should make sure. Start R-studio, and type

install.packages("SqlRender")
library(SqlRender)
translate("SELECT TOP 10 * FROM person;", "postgresql")
## [1] "SELECT  * FROM person LIMIT 10;"

This function uses Java, so if all goes well we know both R and Java have been installed correctly!

Another test is to see if source packages can be built. Run the following R code to install the CohortMethod package from the OHDSI GitHub repository:

install.packages("drat")
install.packages("CohortMethod")