One lesser-known feature is R's ability to use anonymous functions, which are functions without a name. They can be defined inline and are useful in scenarios where you need to pass a function as an argument to another function.

R's ability to interface with other programming languages like C++ and Python is also a lesser-known feature. This enables you to leverage the power of these languages and use R for high-level data analysis and visualization.

Another lesser-known feature is R's support for multiple dispatch, which allows you to define different implementations of a function based on the types of its arguments. This can make your code more flexible and efficient.

R's support for lazy evaluation is often overlooked. Lazy evaluation means that an expression is not evaluated immediately, but only when its value is needed. This can lead to more efficient code execution, especially when dealing with large datasets.