phonics: Phonetic Spelling Algorithms

## Copyright (c) 2015-2019, James P. Howard, II <jh@jameshoward.us>
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#' @title Caverphone
#'
#' @description
#' The Caverphone family of phonetic algorithms
#'
#' @param word string or vector of strings to encode
#' @param maxCodeLen   maximum length of the resulting encodings, in characters
#' @param modified     if \code{TRUE}, use the Caverphone 2 algorithm
#' @param clean if \code{TRUE}, return \code{NA} for unknown alphabetical characters
#'
#' @details
#'
#' The variable \code{maxCodeLen} is the limit on how long the returned
#' Caverphone code should be.  The default is 6, unless \code{modified}
#' is set to \code{TRUE}, then the default is 10.
#'
#' The variable \code{modified} directs \code{caverphone} to use the
#' Caverphone2 method, instead of the original.
#'
#' The \code{caverphone} algorithm is only defined for inputs over the
#' standard English alphabet, \emph{i.e.}, "A-Z.". Non-alphabetical
#' characters are removed from the string in a locale-dependent fashion.
#' This strips spaces, hyphens, and numbers.  Other letters, such as
#' "Ü," may be permissible in the current locale but are unknown to
#' \code{caverphone}.  For inputs outside of its known range, the output is
#' undefined and \code{NA} is returned and a \code{warning} this thrown.
#' If \code{clean} is \code{FALSE}, \code{caverphone} attempts to process the
#' strings.  The default is \code{TRUE}.
#'
#' @return the Caverphone encoded character vector
#'
#' @references
#'
#' David Hood, "Caverphone: Phonetic matching algorithm," Technical
#' Paper CTP060902, University of Otago, New Zealand, 2002.
#'
#' David Hood, "Caverphone Revisited," Technical Paper CTP150804
#' University of Otago, New Zealand, 2004.
#'
#' James P. Howard, II, "Phonetic Spelling Algorithm Implementations
#' for R," \emph{Journal of Statistical Software}, vol. 25, no. 8,
#' (2020), p. 1--21, <10.18637/jss.v095.i08>.
#'
#' @family phonics
#'
#' @examples
#' caverphone("William")
#' caverphone(c("Peter", "Peady"), modified = TRUE)
#' caverphone("Stevenson", maxCodeLen = 4)
#'
#' @export
caverphone <- function(word, maxCodeLen = NULL, modified = FALSE, clean = TRUE) {
    ## From here on, this is a line-for-line translation of the Apache
    ## Commons Caverphone and Caverphone2 implementations, which both
    ## used regular expressions for substantially all of the work.

    ## Set the maxCodeLen if not set
    if(is.null(maxCodeLen))
        if(modified == TRUE)
            maxCodeLen <- 10
        else
            maxCodeLen <- 6

    ## First, uppercase it and test for unprocessable characters
    word <- tolower(word)
    listNulls <- is.null(word)
    listNAs <- is.na(word)
    if(any(nonalpha <- grepl("[^a-z]", word, perl = TRUE)) && clean)
        warning("unknown characters found, results may not be consistent")
    word <- gsub("[^a-z]*", "", word, perl = TRUE)

    if(modified == TRUE)
        word <- caverphone_modified(word)
    else
        word <- caverphone_original(word)

    ## Pad the wording with maxCodeLen 1s and truncate
    ones <- paste(rep(1, maxCodeLen), sep = "", collapse = "")
    word <- gsub("$", ones, word, perl = TRUE)
    word <- substr(word, 1, maxCodeLen)
    word <- gsub(ones, "", word, perl = TRUE)

    ## Yeah, we already processed them, but now get rid of them
    word[listNulls] <- NA
    word[listNAs] <- NA
    if(clean)
        word[nonalpha] <- NA

    return(word)
}

caverphone_original <- function(word) {

    ## Starting and ending special cases
    word <- gsub("^cough", "cou2f", word, perl = TRUE)
    word <- gsub("^rough", "rou2f", word, perl = TRUE)
    word <- gsub("^tough", "tou2f", word, perl = TRUE)
    word <- gsub("^enough", "enou2f", word, perl = TRUE)
    word <- gsub("^gn", "2n", word, perl = TRUE)
    word <- gsub("mb$", "m2", word, perl = TRUE)

    ## Core encodings
    word <- gsub("cq", "2q", word, perl = TRUE)
    word <- gsub("ci", "si", word, perl = TRUE)
    word <- gsub("ce", "se", word, perl = TRUE)
    word <- gsub("cy", "sy", word, perl = TRUE)
    word <- gsub("tch", "2ch", word, perl = TRUE)
    word <- gsub("c", "k", word, perl = TRUE)
    word <- gsub("q", "k", word, perl = TRUE)
    word <- gsub("x", "k", word, perl = TRUE)
    word <- gsub("v", "f", word, perl = TRUE)
    word <- gsub("dg", "2g", word, perl = TRUE)
    word <- gsub("tio", "sio", word, perl = TRUE)
    word <- gsub("tia", "sia", word, perl = TRUE)
    word <- gsub("d", "t", word, perl = TRUE)
    word <- gsub("ph", "fh", word, perl = TRUE)
    word <- gsub("b", "p", word, perl = TRUE)
    word <- gsub("sh", "s2", word, perl = TRUE)
    word <- gsub("z", "s", word, perl = TRUE)
    word <- gsub("^[aeiou]", "A", word, perl = TRUE)
    word <- gsub("[aeiou]", "3", word, perl = TRUE)
    word <- gsub("3gh3", "3kh3", word, perl = TRUE)
    word <- gsub("gh", "22", word, perl = TRUE)
    word <- gsub("g", "k", word, perl = TRUE)
    word <- gsub("ss*", "S", word, perl = TRUE)
    word <- gsub("tt*", "T", word, perl = TRUE)
    word <- gsub("pp*", "P", word, perl = TRUE)
    word <- gsub("kk*", "K", word, perl = TRUE)
    word <- gsub("ff*", "F", word, perl = TRUE)
    word <- gsub("mm*", "M", word, perl = TRUE)
    word <- gsub("nn*", "N", word, perl = TRUE)
    word <- gsub("w3", "W3", word, perl = TRUE)
    word <- gsub("wy", "Wy", word, perl = TRUE)
    word <- gsub("wh3", "Wh3", word, perl = TRUE)
    word <- gsub("why", "Why", word, perl = TRUE)
    word <- gsub("w", "2", word, perl = TRUE)
    word <- gsub("^h", "A", word, perl = TRUE)
    word <- gsub("h", "2", word, perl = TRUE)
    word <- gsub("r3", "R3", word, perl = TRUE)
    word <- gsub("ry", "Ry", word, perl = TRUE)
    word <- gsub("r", "2", word, perl = TRUE)
    word <- gsub("l3", "L3", word, perl = TRUE)
    word <- gsub("ly", "Ly", word, perl = TRUE)
    word <- gsub("l", "2", word, perl = TRUE)
    word <- gsub("j", "y", word, perl = TRUE)
    word <- gsub("y3", "Y3", word, perl = TRUE)
    word <- gsub("y", "2", word, perl = TRUE)
    word <- gsub("[23]", "", word, perl = TRUE)

    return(word)
}

caverphone_modified <- function(word) {

    ## Starting and ending special cases
    word <- gsub("e$", "", word, perl = TRUE)
    word <- gsub("^cough", "cou2f", word, perl = TRUE)
    word <- gsub("^rough", "rou2f", word, perl = TRUE)
    word <- gsub("^tough", "tou2f", word, perl = TRUE)
    word <- gsub("^enough", "enou2f", word, perl = TRUE)
    word <- gsub("^trough", "trou2f", word, perl = TRUE)
    word <- gsub("^gn", "2n", word, perl = TRUE)
    word <- gsub("mb$", "m2", word, perl = TRUE)

    ## Core encodings
    word <- gsub("cq", "2q", word, perl = TRUE)
    word <- gsub("ci", "si", word, perl = TRUE)
    word <- gsub("ce", "se", word, perl = TRUE)
    word <- gsub("cy", "sy", word, perl = TRUE)
    word <- gsub("tch", "2ch", word, perl = TRUE)
    word <- gsub("c", "k", word, perl = TRUE)
    word <- gsub("q", "k", word, perl = TRUE)
    word <- gsub("x", "k", word, perl = TRUE)
    word <- gsub("v", "f", word, perl = TRUE)
    word <- gsub("dg", "2g", word, perl = TRUE)
    word <- gsub("tio", "sio", word, perl = TRUE)
    word <- gsub("tia", "sia", word, perl = TRUE)
    word <- gsub("d", "t", word, perl = TRUE)
    word <- gsub("ph", "fh", word, perl = TRUE)
    word <- gsub("b", "p", word, perl = TRUE)
    word <- gsub("sh", "s2", word, perl = TRUE)
    word <- gsub("z", "s", word, perl = TRUE)
    word <- gsub("^[aeiou]", "A", word, perl = TRUE)
    word <- gsub("[aeiou]", "3", word, perl = TRUE)
    word <- gsub("j", "y", word, perl = TRUE)
    word <- gsub("^y3", "Y3", word, perl = TRUE)
    word <- gsub("^y", "a", word, perl = TRUE)
    word <- gsub("y", "3", word, perl = TRUE)
    word <- gsub("3gh3", "3kh3", word, perl = TRUE)
    word <- gsub("gh", "22", word, perl = TRUE)
    word <- gsub("g", "k", word, perl = TRUE)
    word <- gsub("ss*", "S", word, perl = TRUE)
    word <- gsub("tt*", "T", word, perl = TRUE)
    word <- gsub("pp*", "P", word, perl = TRUE)
    word <- gsub("kk*", "K", word, perl = TRUE)
    word <- gsub("ff*", "F", word, perl = TRUE)
    word <- gsub("mm*", "M", word, perl = TRUE)
    word <- gsub("nn*", "N", word, perl = TRUE)
    word <- gsub("w3", "W3", word, perl = TRUE)
    word <- gsub("wh3", "Wh3", word, perl = TRUE)
    word <- gsub("w$", "3", word, perl = TRUE)
    word <- gsub("w", "2", word, perl = TRUE)
    word <- gsub("^h", "A", word, perl = TRUE)
    word <- gsub("h", "2", word, perl = TRUE)
    word <- gsub("r3", "R3", word, perl = TRUE)
    word <- gsub("r$", "3", word, perl = TRUE)
    word <- gsub("r", "2", word, perl = TRUE)
    word <- gsub("l3", "L3", word, perl = TRUE)
    word <- gsub("l$", "3", word, perl = TRUE)
    word <- gsub("l", "2", word, perl = TRUE)
    word <- gsub("2", "", word, perl = TRUE)
    word <- gsub("3$", "A", word, perl = TRUE)
    word <- gsub("3", "", word, perl = TRUE)

    return(word)
}