Update a Sparse Context Count Environment

Increment or decrement the count of a symbol within a given context stored in an environment-based sparse representation.

Usage

update_env(env, ctx, sym, sign = +1)

Arguments

env

An environment mapping context IDs (`ctx`) to named integer vectors. Each vector represents symbol counts for that context.

ctx

Character. Context identifier key (n-grams).

sym

Character. Symbol/event that follows the context.

sign

Integer. Update direction: - `+1` increments the count (default behavior during training) - `-1` decrements the count (used during detrain or reversal)

Value

Invisibly returns `NULL`. The environment is modified in place.

Details

This function is used as the core update primitive for PPM-style models, where each context (`ctx`) stores a named integer vector of symbol counts.

The update is *sparse*: only symbols with non-zero counts are stored.

Examples

env <- new.env()

# add observations
update_env(env, "A_B", "C", +1)
update_env(env, "A_B", "C", +1)

# decrement
update_env(env, "A_B", "C", -1)

env[["A_B"]]
#> C 
#> 1