Fast lookups using R's evironments, which are implemented using hash tables (vectorised)

vectorised_hash_tables.R

# inspired by https://stackoverflow.com/questions/16782518/is-this-a-good-way-to-make-a-multi-dimensional-dictionary-in-r/16782745#16782745
# and http://broadcast.oreilly.com/2010/03/lookup-performance-in-r.html

hash <- function( ) {
  new.env( hash = TRUE, parent = emptyenv() ) 
}

set <- function(key, val, hash) {
  invisible(mapply(assign, key, val, MoreArgs = list(envir = hash)))
}

lookup <- function(key, hash, use_names = TRUE) {
  sapply(key, get, envir = hash, USE.NAMES = use_names)
}

d = hash()

set(c('a','b'), c(1,2), d)

lookup(c('a','b'), d)
lookup(c('a','b'), d, FALSE)