One feature that I love in R is the ability to write functions that can return multiple values as a list. This is particularly useful when you want to return different types of objects or when you have multiple computations to perform within a function. By returning a list, you can easily access the individual values using named or indexed access, making your code more readable and flexible.

One feature that often goes unnoticed is the ability to work with environments. R allows you to create and manipulate environments, which are like enclosed spaces to store variables and their values. This can be very helpful when you want to create unique and controlled execution contexts or when you need to simulate isolated environments for testing purposes.

Another underrated feature in R is the ability to create custom S3 and S4 classes. While most developers are familiar with base R classes like vectors and data frames, creating your own classes can provide a more intuitive and specialized representation of the data and make your code more expressive and reusable.

R has a powerful set of debugging tools that are often underutilized. The debug() function, for example, allows you to set breakpoints within your code and step through it line by line, inspecting variables and finding bugs quickly. Similarly, the traceback() function can be used to identify the call stack when an error occurs, helping you pinpoint the exact source of the problem.

One of the lesser-known features of R that I find incredibly useful is the ability to work with namespaces. R allows you to define and create your own namespaces, which helps in organizing and managing functions, variables, and packages. By using namespaces, you can avoid naming conflicts and make your code more modular and maintainable.