使用atop时减少线之间的间距

Question

我一直在使用R中的atop和expression为某些数字创建轴标签，因为我需要用斜体字来表示，使用上标，我的标签需要超过两行。

这是我正在使用的一个例子：

plot(c(1:10),ylab="")
mtext(side=2,line=2,expression(atop('Mean height of ', italic(Dicksonia~antarctica)*  ' (m)')))

然而，两条线之间的空间对于我的数字来说太大了。我能减少这个空间吗？

Answer 1

我建议您跳过atop部分并坚持使用标准\n来表示新行。在这种情况下，您可以通过lheight中的图形参数par来控制间距。所以，你可以这样做：

par(lheight=.5) # or adjust to whatever
plot(c(1:10),ylab="")
mtext(side=2,line=2,expression('Mean height of \n', italic(Dicksonia~antarctica)*  ' (m)'))

它也可能与atop一起工作，我无法弄明白！所以关于这一点的任何评论（或其他答案）都是受欢迎的！

Answer 2

尝试在lheight函数中使用par()参数，并稍微修改您的expression()输入：

par(lheight=0.2)   # the default is 1
plot(c(1:10),ylab="")

# Use new line character to separate the lines and 
# apply atop() command to the second part of your expression:
mtext(side=2,line=2,
      expression('Mean height of \n', atop(italic(Dicksonia~antarctica)*  ' (m)')))

Answer 3

There is a solution with using atop() only, as you were exploring first time, but is a bit more verbose than the solution with just using \n as posted by Yannis above.

The main idea is that every time we call atop() within another atop(), the text gets smaller, but also the gap between the lines, so we can use that in our advantage. For your two lines example, we could call atop() two times, one within another, which forces 3 lines, but we set the first line empty (NA or NULL or "" will work), so that the next atop() plots a smaller gap between the lines, but also the text gets smaller. To solve the problem of the text getting smaller, we must employ textstyle(). Well, things get easily verbose, but is nevertheless a solution.

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The original code from the question, illustrating the issue with the wide gap between the two lines of text; on my device is even pushing the first line outside of the "canvas" (I plot it here for comparison reasons, so to see clearly what the proposed solution does):

plot(c(1:10),ylab="")
mtext(side=2,line=2,expression(atop('Mean height of ', italic(Dicksonia~antarctica)*  ' (m)')))

Reduce the gap between the two lines of text with two atop() calls and the textstyle() wraps. I also took the liberty to replac the * ' (m)' with ~ (m), mostly to show that that is possible as well, giving a slightly different visual aspect of the brackets:

plot(c(1:10), ylab = "")
mtext(side = 2, line = 2, 
      expression(atop(NA, atop(textstyle('Mean height of'),
                               textstyle(italic(Dicksonia ~ antarctica) ~ (m))))))

^{Created on 2019-01-15 by the reprex package (v0.2.1)}