我尝试在执行R块以定义大小块选项后评估变量：
---
title: "R Notebook"
output:
pdf_document: default
html_notebook: default
---
```{r setup}
library("tidyverse")
theme_set(theme_bw())
theme_update(strip.background = element_blank())
knitr::opts_chunk$set(out.width = "80%",
out.height = "80%",
eval.after = c("fig.height", "fig.width"))
```
# Example chunk attempting to eval.after
```{r fig.width=figWidth, fig.height=figHeight}
plt <- ggplot(iris,
aes(x = Sepal.Length,
y = Sepal.Width,
color = Petal.Length/Petal.Width)) +
geom_point() +
facet_wrap(~Species, ncol = 1)
figWidth <- 7*max(ggplot2::ggplot_build(plt)$layout$layout$COL)
figHeight <- 3.5*max(ggplot2::ggplot_build(plt)$layout$layout$ROW)
plt
```
错误示例：
