Register metadata behavior for a koma_ts attribute — set_koma_attr

Custom koma_ts attributes (e.g. anker) are combined using default_koma_attr_merge() unless a policy is registered here. The default policy requires both operands' values to be identical and errors otherwise – use this function to define how an attribute should behave under arithmetic (merge), stats::lag(), stats::window(), and stats::na.omit().

Usage

set_koma_attr_policy(
  attr,
  merge = NULL,
  lag = NULL,
  window = NULL,
  na_omit = NULL
)

Arguments

attr: Name of the attribute.
merge: Optional binary merge handler with signature function(left, right, attr, op = NULL, template = NULL).
lag: Optional lag handler with signature function(value, attr, template = NULL, ...).
window: Optional window handler with signature function(value, attr, template = NULL, ...).
na_omit: Optional na.omit handler with signature function(value, attr, template = NULL, ...).

Value

The registered policy, invisibly.

Details

Policies are registered globally, for the current R session: once set, attr is handled the same way for every koma_ts operation, for every pair of series, not just the ones that prompted the call. There is no unset/reset function, so a policy stays in effect until it is overwritten or the session ends. A permissive merge handler (e.g. one that silently drops a mismatch) can mask a genuine bug in an unrelated part of the codebase where that same mismatch should have raised an error – register the narrowest handler that solves your actual case, not a blanket "never error" one.

Examples

# By default, koma_ts arithmetic errors if an attribute's values differ
# between operands (see `default_koma_attr_merge()`) -- e.g. subtracting
# two "rate" series to build an identity like an inflation spread, where
# each side carries its own (different) base-level anchor. A linear
# combination of two series' rates has no single base level to invert
# back to, so here dropping the anchor on mismatch is the right call.
#
# This changes how *all* koma_ts arithmetic handles "anker" for the rest
# of the session (see Details) -- only register this once you've decided
# that "anker" values are never meant to be compared for equality
# elsewhere in your workflow.
set_koma_attr_policy(
  "anker",
  merge = function(left, right, attr, op = NULL, template = NULL) NA
)