r - Lattice 的 `panel.rug` 产生不同的线长度和宽图

Question

当在边距包含 panel.rug() 的点阵中生成宽图时，崎岖边距中的线条长度在 y 轴上比x 轴:

library(lattice)
png(width=800, height=400)
xyplot(Fertility ~ Education, swiss, panel = function(x, y,...) {
  panel.xyplot(x, y, col=1, pch=16)
  panel.rug(x, y, col=1, end= ...)})
dev.off()

我希望 x 轴和 y 轴上的地毯线长度相同，无论绘图的形状如何(注意:现在地毯线仅当绘图为正方形时长度才会相同)。

Answer 1

使用lattice，只需将panel.rug使用的坐标系从默认值(“npc”)更改为“snpc":

library(lattice)

## png(width=800, height=400)
xyplot(Fertility ~ Education, swiss, panel = function(x, y,...) {
  panel.xyplot(x, y, col=1, pch=16)
  panel.rug(x = x, y = y,  
            x.units = rep("snpc", 2),  y.units = rep("snpc", 2), 
            col=1, end= ...)
})
## dev.off()

要了解为什么这会得到您想要的结果，请参阅?unit以获取这两个坐标系含义的描述:

 Possible ‘units’ (coordinate systems) are:

 ‘"npc"’ Normalised Parent Coordinates (the default).  The origin
      of the viewport is (0, 0) and the viewport has a width and
      height of 1 unit.  For example, (0.5, 0.5) is the centre of
      the viewport.

 ‘"snpc"’ Square Normalised Parent Coordinates.  Same as Normalised
      Parent Coordinates, except gives the same answer for
      horizontal and vertical locations/dimensions.  It uses the
      _lesser_ of npc-width and npc-height.  This is useful for
      making things which are a proportion of the viewport, but
      have to be square (or have a fixed aspect ratio).