为什么第二个ggplot不会出现使用knitr和grid？

我正在尝试使用knitr包含ggplot2使用修改的图表创建文档grid.

在下面的例子中,应该是2绘出使用既diamonds包括在数据集ggplot2:第一个显示切割与颜色和切断第二节目与清晰度.相反,后面的情节重复两次.根figure目录中根本不生成第一个图.

\documentclass{article}

\begin{document}

<>=
library(ggplot2)
library(grid)
theme_update(plot.margin = unit(c(1.5, 2, 1, 1), 'lines'))

# Create plot with color

p = ggplot(diamonds,aes(cut,fill = color)) + geom_bar(position = 'fill') + annotate('text', label = as.character(table(diamonds$cut)), x = 1:5, y = Inf, vjust = -1)
gt = ggplot_gtable(ggplot_build(p))
gt$layout$clip[gt$layout$name == 'panel'] = 'off'
grid.draw(gt)

# Create plot with clarity

q = ggplot(diamonds,aes(cut,fill = clarity)) + geom_bar(position = 'fill') + annotate('text', label = as.character(table(diamonds$cut)), x = 1:5, y = Inf, vjust = -1)
gs = ggplot_gtable(ggplot_build(q))
gs$layout$clip[gs$layout$name == 'panel'] = 'off'
grid.draw(gs)
@

\end{document}

重要的是,如果我删除以下行:

gt = ggplot_gtable(ggplot_build(p))
gt$layout$clip[gt$layout$name == 'panel'] = 'off'
grid.draw(gt)

从这两个数字来看,它们都将正确生成,但注释将被切断.

是什么导致了这个问题,更重要的是,我该如何修复它？

谢谢!

从评论中添加代码

我grid.newpage()在第二个绘图之前添加了一个允许两个渲染.还必须调整边距以获得要显示的注释.

你的代码是

\documentclass{article}

\begin{document}

<< fig.cap = c('color', 'clarity')>>=
library(ggplot2)
library(grid)

# Create plot with color

p = ggplot(diamonds,aes(cut,fill = color)) + geom_bar(position = 'fill') + annotate('text', label = as.character(table(diamonds$cut)), x = 1:5, y = Inf, vjust = -1) + 
theme(plot.margin=unit( c(2,1,1,1), "lines") ) ### added

gt = ggplot_gtable(ggplot_build(p))
gt$layout$clip[gt$layout$name == 'panel'] = 'off'
grid.draw(gt)

# Create plot with clarity

q = ggplot(diamonds,aes(cut,fill = clarity)) + geom_bar(position = 'fill') + annotate('text', label = as.character(table(diamonds$cut)), x = 1:5, y = Inf, vjust = -1) + 
theme(plot.margin=unit( c(2,1,1,1), "lines") ) ### added

gs = ggplot_gtable(ggplot_build(q))
gs$layout$clip[gs$layout$name == 'panel'] = 'off'
grid.newpage() ## This is the extra line
grid.draw(gs)
@

\end{document}