R/log_transform.R

In anchored-inversion/examples.R: Anchored Inversion Client

## Log transformation: transform betwen (-Inf, Inf) and (lower, Inf) and take care
## of extreme values.  Forward: (lower, Inf) --> (-Inf, Inf) Reverse: (-Inf, Inf)
## --> (lower, Inf)

#' Log transformation.
#'
#' Transform a real number on \code{[lower, Inf)}
#' to the whole real line, or reversely.
#'
#' @param x
#'      Numerical.
#' @param lower
#'      Numerical.
#' @param reverse
#'      Reverse transform?
#'
#' @return
#'      If \code{reverse} is \code{TRUE}, return
#'      \code{log(x - lower)}.
#'      If \code{reverse} is \code{FALSE}, return
#'      \code{lower + exp(x)}.
#'
#' @export
log_transform <- function(x, lower = 0, reverse = FALSE) {
    if (reverse) {
        z <- lower + exp(x)
    } else {
        idx <- which(is.finite(x) & (x <= lower))
        if (length(idx)) {
            warning("some inputs are below the lower bound")
            x[idx] <- NA
        }
        z <- log(x - lower)
    }
    z
}