A shallow copy in R creates a new object that references the same underlying data as the original object. Changes made to one object will be reflected in the other. In contrast, a deep copy creates a new object with its own independent copy of the data. Changes made to one object will not affect the other.

Shallow copy is typically performed through assignment or by passing an object as an argument to a function, while deep copy can be achieved using functions like 'copy()' from the 'base' package or using the 'cpy()' function from the 'data.table' package.

Creating deep copies can be computationally expensive, especially for large objects, so understanding the distinction is important for memory management and avoiding unintended side effects.