#  strwidth2lines
#'
#' Calculate width of a character string in number of lines
#'
#' Convert `stringwidth` units to number of (margin) lines
#'
#' @param s A character or expression vector whose length is to be calculated
#'
#' @param ... additional information used by `strwidth`, such as
#'    `cex`
#'
#' @export
#' @importFrom graphics strwidth
#'
#' @return
#' Maximum string width in units of margin lines
#'
#' @author
#' Aimee Teo Broman
#'
#' @examples
#' p <- par(no.readonly = TRUE)
#' string <- sapply(sample(1:20,15,replace=TRUE),
#'          function(a) paste(LETTERS[1:a], collapse=""))
#' nlines <- strwidth2lines(string)
#' mar <- par("mar")
#' par(mar=c(mar[1],nlines+0.1,mar[3:4]))
#'   plot(1:length(string),1:length(string),yaxt="n", ylab="")
#'   axis(side=2, at=seq_along(string), lab=string, las=1)
#' par(p)
#' nlines <- strwidth2lines(string,cex=1.5)
#' par(mar=c(mar[1:3],nlines+0.1))
#'   plot(1:length(string),1:length(string),ylab="")
#'   mgp <- par("mgp")
#'   axis(side = 4, at=seq_along(string),
#'     labels = string ,las=1, hadj=1,
#'        mgp=c(mgp[1],nlines,mgp[3]),cex.axis=1.5)
#' par(p)
strwidth2lines <- function(s, ...){
    (max(strwidth(s, units="inch", ...))/
     par("cin")[2]+par("mgp")[2])*par("cex")
}
