Knitr and Figure Caption in HTML

Question

knitr defines the argument fig.cap as

fig.cap: (NULL; character) figure caption to be used in a figure environment in LaTeX (in \caption{}); if NULL or NA, it will be ignored, otherwise a figure environment will be used for the plots in the chunk (output in \begin{figure} and \end{figure})

However, for HTML output the following works:

---
title: "Caption Test"
author: "Some Author"
date: "February 18, 2016"
output: html_document
---

```{r}
library(ggplot2)
```

```{r, fig.cap = c("This is caption 1", "This is caption 2")}
## Plot 1
qplot(carat, price, data = diamonds)

## Plot 2
qplot(carat, depth, data = diamonds)
```

meaning, each figures gets its correct caption defined in the code chunk argument fig.cap = c("Caption 1", "Caption 2")

However, it is challenging to keep track of captions -especially if long- when they are placed inside the chunk options. Besides creating two separate chunks for each figure with captions inserted outside of the chunk, are there other options?

Answer 1

You can set eval.after="fig.cap" so that figure captions are evaluated after the chunk is run. That way, you can define your captions inside the chunk.

---
title: "Caption Test"
author: "Some Author"
date: "February 18, 2016"
output: html_document
---

```{r}
library(ggplot2)
library(knitr)
opts_knit$set(eval.after = 'fig.cap')
```

```{r, fig.cap = cap}
## Plot 1
qplot(carat, price, data = diamonds)
cap <- "This is caption 1"

## Plot 2
qplot(carat, depth, data = diamonds)

cap <- c(cap, "This is caption 2")
```