r - 如何引用稍后通过 bookdown 显示的绘图？

Question

This section R Markdown Cookbook 的 内容展示了如何创建绘图并稍后在文档中显示它:

---
output: bookdown::pdf_document2
---

We generate a plot in this code chunk but do not show it:

```{r cars-plot, dev='png', fig.show='hide'}
plot(cars)
```

After another paragraph, we introduce the plot:

![A nice plot.](`r knitr::fig_chunk('cars-plot', 'png')`)

我遇到的问题是我无法在文本中引用该图。请参阅以下代码和输出:

---
output: bookdown::pdf_document2
---

We generate a plot in this code chunk but do not show it:

```{r cars-plot, dev='png', fig.show='hide'}
plot(cars)
```

Here's a reference to this plot: figure \@ref(fig:cars-plot).

After another paragraph, we introduce the plot:

![A nice plot.](`r knitr::fig_chunk('cars-plot', 'png')`)

请注意，如果我立即显示该图，则引用效果很好:

---
output: bookdown::pdf_document2
---

We generate a plot in this code chunk but do not show it:

```{r cars-plot, fig.cap="A nice plot."}
plot(cars)
```

Here's a reference to this plot: figure \@ref(fig:cars-plot).

如何稍后显示绘图但仍然能够引用它？我知道我可以简单地将 block 移动到我想要绘图出现的位置，但这对我来说并不理想。

Answer 1

在后面的 block 中使用ref.label，并在图形引用中引用后面的 block 名称。

---
output: bookdown::pdf_document2
---

We generate a plot in this code chunk but do not show it:

```{r cars-plot, dev='png', fig.show='hide'}
plot(cars)
```

Here's a reference to this plot: figure \@ref(fig:cars-plot-show).

After another paragraph, we introduce the plot:

```{r cars-plot-show, ref.label="cars-plot", fig.cap="A Nice Plot"}

```