Dividewhere

Dividewhere is a term used in discussions of data processing and programming to describe a composite operation that first divides a collection into subgroups and then applies separate filtering conditions within each subgroup. It is not an official standard in mainstream mathematics or database theory, but it appears in tutorials, language design discussions, and exploratory notes as a way to express a two-step data transformation in a concise form.

Definition and concept

In its simplest form, dividewhere takes a dataset and two components: a division function that assigns each element to a partition (for example, a type or a boolean split), and a separate where condition for each partition. The operation yields two (or more) filtered subsets, one for each partition, where elements must satisfy the corresponding where predicate. More generally, dividewhere can be parameterized to support multiple partitions and associated predicates.

Example

Consider a dataset of records with a field type that can be A or B, and two predicates pA and pB. A dividewhere operation might produce two result sets: A = {records | type = 'A' and pA(record)} and B = {records | type = 'B' and pB(record)}.

Applications

Dividewhere is discussed as a pattern for data segmentation, feature engineering, and query construction where partition-specific filters are natural. It aligns with ideas from partitioning, filter-then-join strategies, and multi-branch dataflows. In practice, it can be implemented in procedural code or within domain-specific languages by combining partitioning with conditional filtering.

History and reception

Dividewhere lacks a formal, standardized definition in widely used references. It is primarily encountered as a descriptive term in learning resources and design discussions about expressive data-query and data-flow constructs. Critics note potential ambiguity and the availability of alternative, clearer formulations in established paradigms.

See also

Partition, filter, partitioning, data flow, domain-specific language.