xswithFilterpmapf

xswithFilterpmapf is a functional programming utility described as a composite operation that filters a sequence and then maps the result, typically with parallelism for the mapping step. It is conceived as a single, higher-order operation that combines two common data transformations: filtering and mapping.

Formal concept and signature

In a typical interpretation, xswithFilterpmapf takes a collection xs, a predicate p, and a function f, and returns a new collection by keeping elements of xs that satisfy p and then applying f to each kept element. A common sequential version is like: xswithFilterpmapf xs p f = map f (filter p xs). If the suffix pmapf implies parallel mapping, an alternative form uses a parallel map: xswithFilterpmapf xs p f = parallelMap f (filter p xs). The exact implementation depends on the language and runtime, but the intent is to fuse filtering with a subsequent transformation.

Semantics and evaluation

The operation preserves the order of elements that pass the predicate, unless the underlying parallel map reorders results. It has a time complexity proportional to the input size, typically O(n) for filtering plus O(m) for mapping, where m is the number of elements that pass p. Memory usage is driven by the size of the output and any intermediate structures. In lazy languages, the combination can be evaluated in a single pass if fusion is supported, reducing intermediate allocations.

Usage and considerations

xswithFilterpmapf is useful when you need to discard unwanted items early and apply a transformation to the remaining items, potentially leveraging parallelism to speed up the mapping step. It is commonly cited in discussions of map-filter fusion, data pipelines, and parallel data processing.

See also: filter, map, withFilter, pmap (parallel map).