R/getTicks.R

In gforge/forestplot: Advanced Forest Plot Using 'grid' Graphics

#' Ticks for plot axis
#'
#' Gets the ticks in a formatted version. This is since I'm not always
#' that fond of just pretty(1:10/5). In exponential form the ticks are
#' determined from the 2-base, meaning that you get an intuitive feeling
#' for when the value is doubled.
#'
#' This function is far from perfect and I recommend specifying yourself
#' the ticks that you want.
#'
#' @param low lower bound, can be a single number or a vector
#' @param high upper bound - optional, you can just have all data in the low variable
#' @param clip if the ci are clipped
#' @param exp If the value should be in exponential form (default)
#' @param digits Number of digits - used in exp mode
#' @return \code{vector} Returns a vector with the ticks
#'
#' @example inst/examples/getTicks_example.R
#' @export
getTicks <- function(low,
                     high = low,
                     clip = c(-Inf, Inf),
                     exp = FALSE,
                     digits = 0) {
  # Get the right ticks
  lowest <- max(min(low, na.rm = TRUE), clip[1])
  bottom <- floor(lowest * 2) / 2
  if (bottom == 0 && exp) {
    bottom <- 2^(round(log2(lowest) * 2) / 2)
  }

  highest <- min(max(high, na.rm = TRUE), clip[2])
  roof <- ceiling(highest * 2) / 2
  if (exp == FALSE) {
    resolution <- roof - bottom

    if (resolution > 20) {
      bottom <- floor(bottom)
      roof <- ceiling(roof)
      xticks <- seq(from = bottom, to = roof, by = 10^floor(log10(resolution)) / 4)
    } else if (resolution > 6) {
      bottom <- floor(bottom)
      roof <- ceiling(roof)
      xticks <- seq(from = bottom, to = roof, by = 1)
    } else if (resolution <= 1) {
      decimals <- -ceiling(log10(resolution)) + 1
      bottom <- floor(lowest * 2 * 10^decimals) / 2 / 10^decimals
      roof <- ceiling(highest * 2 * 10^decimals) / 2 / 10^decimals
      xticks <- seq(from = bottom, to = roof, by = 10^-decimals / 4)
      if (length(xticks) <= 3) {
        xticks <- seq(from = bottom, to = roof, by = 10^-decimals / 8)
      }
    } else {
      bottom <- floor(bottom * 2) / 2
      roof <- ceiling(roof * 2) / 2
      xticks <- seq(from = bottom, to = roof, by = .5)
    }

    if (!bottom %in% xticks) {
      xticks <- c(bottom, xticks)
    }
    if (!roof %in% xticks) {
      xticks <- c(xticks, roof)
    }
  } else {
    if (bottom <= 0) {
      stop("You can't have an exponential scale that goes <= 0, bottom = '", bottom, "'")
    }

    xticks <- c()
    increase_by <- 1
    if (abs(bottom - roof) < 3) {
      # A regular log. scale wont really work :-(
      # return(seq(from = bottom, to = roof, by = 0.5))
      increase_by <- 0.5
    }

    if (bottom < 1) {
      xticks <- append(xticks, round(rev(2^seq(from = 0, to = log2(bottom), by = -increase_by)), digits + 1))
    }

    if (roof > 1) {
      xticks <- unique(append(xticks, round(2^seq(from = 0, to = log2(roof), by = increase_by), digits)))
    }
  }

  # Choose the one that is number wise the closest
  if (abs(lowest - xticks[1]) >= abs(lowest - xticks[2])) {
    xticks <- xticks[-1]
  }

  if (abs(highest - xticks[length(xticks)]) >= abs(highest - xticks[length(xticks) - 1])) {
    xticks <- xticks[-length(xticks)]
  }

  return(xticks)
}