## Copyright (c) 2015-2019, James P. Howard, II <jh@jameshoward.us>
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#' @title Lein Name Coding
#'
#' @description
#' The Lein name coding procedure.
#'
#' @param word string or vector of strings to encode
#' @param maxCodeLen maximum length of the resulting encodings, in characters
#' @param clean if \code{TRUE}, return \code{NA} for unknown alphabetical characters
#'
#' @details
#'
#' The variable \code{word} is the name to be encoded. The variable
#' \code{maxCodeLen} is the limit on how long the returned name code
#' should be. The default is 4.
#'
#' The \code{lein} 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{lein}. 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{lein} attempts to process the
#' strings. The default is \code{TRUE}.
#'
#' @return the Lein encoded character vector
#'
#' @references
#'
#' 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>.
#'
#' Billy T. Lynch and William L. Arends. "Selection of surname coding
#' procedure for the SRS record linkage system." United States
#' Department of Agriculture, Sample Survey Research Branch, Research
#' Division, Washington, 1977.
#'
#' @family phonics
#'
#' @examples
#' lein("William")
#' lein(c("Peter", "Peady"))
#' lein("Stevenson", maxCodeLen = 8)
#'
#' @export
lein <- function(word, maxCodeLen = 4, clean = TRUE) {
## First, uppercase it and test for unprocessable characters
word <- toupper(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)
## First character of key = first character of name
first <- substr(word, 1, 1)
word <- substr(word, 2, nchar(word))
## Delete vowels and Y, W, and H
word <- gsub("A|E|I|O|U|Y|W|H", "", word, perl = TRUE)
## Remove duplicate consecutive characters
word <- gsub("([A-Z])\\1+", "\\1", word, perl = TRUE)
## D, T -> 1
word <- gsub("D|T", "1", word, perl = TRUE)
## M, N -> 2
word <- gsub("M|N", "2", word, perl = TRUE)
## L, R -> 3
word <- gsub("L|R", "3", word, perl = TRUE)
## B, F, P, V -> 4
word <- gsub("B|F|P|V", "4", word, perl = TRUE)
## C, J, K, G, Q, S, X, Z -> 5
word <- gsub("C|J|K|G|Q|S|X|Z", "5", word, perl = TRUE)
## Append word except for first character to first
word <- paste(first, word, sep = "")
## Zero-pad and truncate to requested length
word <- gsub("$", paste(rep(0, maxCodeLen), collapse = ""), word, perl = TRUE)
word <- substr(word, 1, maxCodeLen)
## Manage some edge cases
word <- sub("0000", "", 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)
}
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