R/is.fixed.r

In dartR: Importing and Analysing 'SNP' and 'Silicodart' Data Generated by Genome-Wide Restriction Fragment Analysis

#' Tests if two populations are fixed at a given locus
#'
#' This script compares two percent allele frequencies
#' and reports TRUE if they represent a fixed difference, FALSE otherwise.
#'
#' A fixed difference at a locus occurs when two populations share no alleles,
#'  noting that SNPs are biallelic (ploidy=2).
#' Tolerance in the definition of a fixed difference is provided by the t
#'  parameter. For example, t=0.05 means that SNP allele frequencies of 95,5 and
#'  5,95 percent will be reported as fixed (TRUE).
#'
#' @param s1 Percentage SNP allele or sequence tag frequency for the first 
#' population [required].
#' @param s2 Percentage SNP allele or sequence tag frequency for the second 
#' population [required].
#' @param tloc Threshold value for tolerance in when a difference is regarded as
#'  fixed [default 0].
#' @return TRUE (fixed difference) or FALSE (alleles shared) or NA (one or both 
#' s1 or s2 missing)
#' @author Custodian: Arthur Georges (bugs? Post to
#'  \url{https://groups.google.com/d/forum/dartr})
#' @export
#' @examples
#' is.fixed(s1=100, s2=0, tloc=0)
#' is.fixed(96, 4, tloc=0.05)
#' @seealso \code{\link{gl.fixed.diff}}

is.fixed <- function(s1, 
                     s2, 
                     tloc = 0) {
    if (is.na(s1) | is.na(s2)) {
        result <- NA
    } else {
        # Transform to fixed, if outside tollerance
        if (s1 <= tloc * 100) {
            s1 <- 0
        }
        if (s1 >= 100 - tloc * 100) {
            s1 <- 100
        }
        if (s2 <= tloc * 100) {
            s2 <- 0
        }
        if (s2 >= 100 - tloc * 100) {
            s2 <- 100
        }
        # Score
        result <- 0
        if ((s1 == 0) & (s2 == 100)) {
            result <- 1
        }
        if ((s1 == 100) & (s2 == 0)) {
            result <- 1
        }
    }
    return(result)
}

# Test function is.fixed(0,100) is.fixed(100,0) is.fixed(80,0) is.fixed(100,NA) 
#is.fixed(0,NA) is.fixed(NA,0) is.fixed(NaN,100)
# is.fixed(NaN,0) is.fixed(100,NaN) is.fixed(0,NaN) is.fixed(NaN,NaN) 
#is.fixed(NA,NA) is.fixed(50,50,tloc=0.05)