r - 获取日志空间中的边距线位置

Question

在previous question中，我询问了如何获取用户坐标中的边界线位置。我以line2user函数的形式收到了一个很好的答案。但是，当x轴或y轴处于对数刻度时，我无法弄清楚如何修改该功能以使其工作。

我做了一些修改以适应对数刻度轴:

line2user <- function(line, side, log = "") {
  lh <- par('cin')[2] * par('cex') * par('lheight')
  x_off <- diff(grconvertX(0:1, 'inches', 'user'))
  y_off <- diff(grconvertY(0:1, 'inches', 'user'))
  usr <- par('usr') ## Added by me
  if (grepl("x", log)) usr[1:2] <- 10^usr[1:2] ## Added by me
  if (grepl("y", log)) usr[3:4] <- 10^usr[3:4] ## Added by me
  switch(side,
         `1` = usr[3] - line * y_off * lh,
         `2` = usr[1] - line * x_off * lh,
         `3` = usr[4] + line * y_off * lh,
         `4` = usr[2] + line * x_off * lh,
         stop("Side must be 1, 2, 3, or 4", call.=FALSE))
}

但是，我无法弄清楚如何正确调整 xoff和 yoff变量以绘制正确的线条。插图:

setup_plot <- function(log = "") {
  par(mar = c(2, 10, 2, 2), oma = rep(2, 4))
  plot.new()
  plot.window(xlim = c(1, 10), ylim = c(1, 10), log = log)
  box(which = "plot", lwd = 2, col = "gray40")
  box(which = "figure", lwd = 2, col = "darkred")
  box(which = "outer", lwd = 2, col = "darkgreen")
  text(x = 0.5, y = 0.5, 
       labels = "Plot Region", 
       col = "gray40", font = 2)
  mtext(side = 3, text = "Figure region", line = 0.5, col = "darkred", font = 2)
  mtext(side = 3, text = "Device region", line = 2.5, col = "darkgreen", font = 2)
  for (i in 0:9) {
    mtext(side = 2, col = "darkred", text = paste0("Line", i), line = i)
  }
}

setup_plot(log = "x")
abline(v=line2user(line=0:9, side=2, log = "x"), xpd=TRUE, lty=2)

考虑以下示例后，压缩线才有意义:

plot(10)
diff(grconvertX(0:1, 'inches', 'user'))
## [1] 0.08121573 (on my device)

plot(10, log = "x")
diff(grconvertX(0:1, 'inches', 'user'))
## [1] 0.0297354 (on my device)

使用对数刻度轴时，如何获得正确的 x_off和 y_off值？

Answer 1

这是适用于对数刻度和线性刻度轴的版本。诀窍是用npc坐标而不是user坐标表示线位置，因为当轴在对数刻度上时，后者当然不是线性的。

line2user <- function(line, side) {
  lh <- par('cin')[2] * par('cex') * par('lheight')
  x_off <- diff(grconvertX(c(0, lh), 'inches', 'npc'))
  y_off <- diff(grconvertY(c(0, lh), 'inches', 'npc'))
  switch(side,
         `1` = grconvertY(-line * y_off, 'npc', 'user'),
         `2` = grconvertX(-line * x_off, 'npc', 'user'),
         `3` = grconvertY(1 + line * y_off, 'npc', 'user'),
         `4` = grconvertX(1 + line * x_off, 'npc', 'user'),
         stop("Side must be 1, 2, 3, or 4", call.=FALSE))
}

以下是一些示例，它们通过 setup_plot应用于您的 mar=c(5, 5, 5, 5):

setup_plot()
axis(1, line=5)
axis(2, line=5)
abline(h=line2user(0:4, 1), lty=3, xpd=TRUE)
abline(v=line2user(0:4, 2), lty=3, xpd=TRUE)
abline(h=line2user(0:4, 3), lty=3, xpd=TRUE)
abline(v=line2user(0:4, 4), lty=3, xpd=TRUE)

setup_plot(log='x')
axis(1, line=5)
axis(2, line=5)
abline(h=line2user(0:4, 1), lty=3, xpd=TRUE)
abline(v=line2user(0:4, 2), lty=3, xpd=TRUE)
abline(h=line2user(0:4, 3), lty=3, xpd=TRUE)
abline(v=line2user(0:4, 4), lty=3, xpd=TRUE)

setup_plot(log='y')
axis(1, line=5)
axis(2, line=5)
abline(h=line2user(0:4, 1), lty=3, xpd=TRUE)
abline(v=line2user(0:4, 2), lty=3, xpd=TRUE)
abline(h=line2user(0:4, 3), lty=3, xpd=TRUE)
abline(v=line2user(0:4, 4), lty=3, xpd=TRUE)

setup_plot(log='xy')
axis(1, line=5)
axis(2, line=5)
abline(h=line2user(0:4, 1), lty=3, xpd=TRUE)
abline(v=line2user(0:4, 2), lty=3, xpd=TRUE)
abline(h=line2user(0:4, 3), lty=3, xpd=TRUE)
abline(v=line2user(0:4, 4), lty=3, xpd=TRUE)