README.md
In r2r: R-Object to R-Object Hash Maps

r2r

r2r provides a flexible implementation of hash tables in R, allowing for:

arbitrary R objects as keys and values,
arbitrary key comparison and hash functions,
customizable behaviour (throw or return a default value) on missing key exceptions.

You can install the development version of r2r from GitHub with:

# install.packages("devtools")
devtools::install_github("vgherard/r2r")

library(r2r)
m <- hashmap()

# Insert and query a single key-value pair
m[[ "user" ]] <- "vgherard"
m[[ "user" ]]
#> [1] "vgherard"

# Insert and query multiple key-value pairs
m[ c(1, 2, 3) ] <- c("one", "two", "three")
m[ c(1, 3) ]
#> [[1]]
#> [1] "one"
#> 
#> [[2]]
#> [1] "three"

# Keys and values can be arbitrary R objects
m[[ lm(mpg ~ wt, mtcars) ]] <- c(TRUE, FALSE, TRUE)
m[[ lm(mpg ~ wt, mtcars) ]]
#> [1]  TRUE FALSE  TRUE

For further details, including an introductory vignette illustrating the features of r2r hash maps, you can consult the r2r website. If you encounter a bug, want to suggest a feature or need further help, you can open a GitHub issue.

Comparison with `hash`

CRAN package {hash} also offers an implementation of hash tables based on R environments. The two tables below offer a comparison between {r2r} and {hash} (for more details, see the benchmarks Vignette)

| Feature | r2r | hash | |:---------------------------------------:|:-------------:|:-------------:| | Basic data structure | R environment | R environment | | Arbitrary type keys | X | | | Arbitrary type values | X | X | | Arbitrary hash function | X | | | Arbitrary key comparison function | X | | | Throw or return default on missing keys | X | | | Hash table inversion | | X |

Features supported by {r2r} and {hash}.

| Task | Comparison | |:-------------:|:---------------------:| | Key insertion | {r2r} \~ {hash} | | Key query | {r2r} < {hash} | | Key deletion | {r2r} << {hash} |

Performances of {r2r} and {hash} for basic hash table operations.