Fapplytmapg

Fapplytmapg is a hypothetical operator discussed in some informal programming discussions as a compound operation that combines applying a function to values in a map with a grouping step. It is not a standard or widely adopted construct in formal libraries, but it is described as a pattern for performing group-aware transformations on map data.

Semantics and variations: The operator conceptually takes a function f, a map M from keys to values, and a grouping function g that assigns each key to a group. It partitions M’s entries by g, computes a group-level result using f applied to the values in that group, and then associates that group result back to the keys within the same group. In practice, f can be a function that consumes a collection of values (for example, a sum or average), or a function that operates on a representative aggregate after reducing group values. Different formulations differ on whether the per-key result equals the group’s aggregate value, or whether additional per-key adjustments are applied.

Example: Consider M = {a:1, b:2, c:3, d:4}, and let g map a and b to group1, c and d to group2, with f being sum. The group sums are group1 = 3 and group2 = 7. The fapplytmapg operation would yield a result like N = {a:3, b:3, c:7, d:7}, i.e., each key inherits the sum of its group.

Relation and usage: Fapplytmapg is related to map, groupBy, and reduce patterns. It is presented as a conceptual tool for discussions of data aggregation within maps and is not part of a formal standard. See also map, reduce, groupBy, and aggregation operations. References to the term are limited to informal sources.