独立于行分面数控制 ggplot2 分面高度

Question

问题

ggplot2/knitr 强制绘图（在 LaTeX 中）具有默认纵横比。具有不同面数的两个图会导致面高不同的图。这不好。

我正在寻找一种解决方案，它可以独立于行分面的数量来控制 ggplot2 分面高度。

9 月 9 日编辑： 解决方案应该在一个块中工作，因为两个图都在一个块中（如示例代码中所示）。所以调整 knitr 的图形相关块选项是不可行的，因为块选项同样适用于两个图。

解决方案 - 但有问题

将每个图放入gridExtra 框并根据刻面数量缩放其高度，从而生成不再不同的刻面高度：更好但不完美。

• 绘图显示在页面上的页边距过大，即使下面还有剩余的文字，所以绘图应该更靠近。
• 似乎被此操作的地块被裁剪了。

是否有更智能且无问题的解决方案，可以独立于行分面数控制 ggplot2 分面高度？

\documentclass[a4paper]{article}
\usepackage[margin=1in]{geometry}

\begin{document}

<<setup, results='asis', message=FALSE, echo=FALSE>>=
require(ggplot2)
require(gridExtra)

### Generate two data frames

# Data frame with 2 classes
db.small = data.frame (
  class = as.factor(c(rep("A", 12), rep("B", 12))),
  month = as.factor(rep(1:12, 2)),
  value = runif(2*12, 0, 100)
  )

# Data frame with 5 classes
db.large = data.frame (
  class = as.factor(c(rep("A", 12), rep("B", 12), rep("C", 12), rep("C", 12), rep("D", 12))),
  month = as.factor(rep(1:12, 5)),
  value = runif(5*12, 0, 100)
)

# Generate plots
plot1 = ggplot(db.small, aes(month, value)) + geom_bar(stat="identity") + facet_grid(class ~ .) + ylim(c(0, 100))
plot2 = ggplot(db.large, aes(month, value)) + geom_bar(stat="identity") + facet_grid(class ~ .) + ylim(c(0, 100))
@

\section{Before: Native plots without modification}
Ggplot2/knitr forces both plots to have the default aspect ratio. As both plots have different number of facets the result is that the facet heights are different. This is not nice.

<<before, results='asis', message=FALSE, echo=FALSE, out.width="0.6\\linewidth">>=
print(plot1)
print(plot2)
@

\pagebreak
\section{After: Plots with modification}
Putting each plot into a gridExtra box and scaling it's height with the number of facets, results in facet heights which are no longer different: nicer but not perfect, see problems below.

<<After, results='asis', message=FALSE, echo=FALSE, out.width="0.6\\linewidth">>=
# Calculate number of facets for the two plots
db.small.numberfacets = length(unique(db.small$class))
db.large.numberfacets = length(unique(db.large$class))

# Define heights for modification of plots
facet.height = 4
other.height = 2

plot1 = plot1 + theme( plot.margin = unit(c(0, 0, 0, 0), "cm"))
plot2 = plot2 + theme( plot.margin = unit(c(0, 0, 0, 0), "cm"))

# Put plots inside a gridExtra box and change height plots
grid.arrange(arrangeGrob(plot1, heights=unit(db.small.numberfacets*facet.height+other.height, "cm")), nrow=1)
grid.arrange(arrangeGrob(plot2, heights=unit(db.large.numberfacets*facet.height+other.height, "cm")), nrow=1)
@


2 Problems:
\begin{itemize}
\item Plots appear on the page with too much margin, even there's remaining text below so plots shall move more closer.
\item Seems the second plot is cropped, see the x-axis label.
\end{itemize}

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\end{document}

pdf 输出：

Answer 1

你知道 knitr chunk options 可以接受任意 R 表达式吗？ example 40 展示了如何动态计算 fig.width 和 fig.height。

对于您的情况，您可以根据因子变量中用于分面的级别数为fig.height 分配一个值。例如，

\documentclass{article}

\begin{document}
<<setup>>=
library(ggplot2)
calc_height = function(f) length(levels(f))
p = ggplot(diamonds, aes(color)) + geom_bar()
@

<<test-a, fig.width=7, fig.height=calc_height(diamonds$cut)>>==
p + facet_grid(cut ~ .)
@

<<test-b, fig.width=7, fig.height=calc_height(diamonds$clarity)>>==
p + facet_grid(clarity ~ .)
@

\end{document}

输出：