TakeLast

TakeLast is a term used in programming to describe an operation that yields the final N elements of a sequence, list, array, or stream while preserving their original order. The function takes a single integer parameter n and returns a collection containing the last n elements. If the source contains fewer than n elements, the entire source is returned.

In finite collections, takeLast can be implemented by indexing or slicing the end of the collection. In streaming or reactive APIs, takeLast is typically a terminal operator that buffers the last n elements as they arrive and emits them only after the input completes; for unbounded or infinite streams, this means no output is produced until completion, and some APIs provide alternative windowed variants.

Edge cases include n <= 0, which yields an empty collection, and n >= size, which yields the whole source. The behavior for streams depends on the API: it may require completion to emit results or provide a failure mode for non-terminating inputs.

Common usage examples illustrate its cross-language presence. In Kotlin, list.takeLast(3) returns the last three elements. In JavaScript, arr.slice(-3) returns a new array with the last three elements. In ReactiveX libraries, observable.takeLast(3) returns an observable that emits the last three items when the source completes.

Related concepts include take, drop, and tail, as well as takeRight in languages that distinguish between end-based and index-based operations. TakeLast is a widely used pattern for extracting trailing elements from a collection or stream.