Rmarkdown：如何显示块的部分输出？

Question

我有一个 Rmarkdown 文档，我想只显示代码块的部分输出。

例如，考虑以下情况：

```{r echo=1:2, eval=-2, collapse=TRUE}
mod <- lm(speed ~ dist, data = cars)
summary(mod)
out <- capture.output(summary(mod))
cat(c("[...]", out[9:12], "[...]"), sep = "\n")
```

产生

mod <- lm(speed ~ dist, data = cars)
## summary(mod)
## [...]
## Coefficients:
##             Estimate Std. Error t value         Pr(>|t|)    
## (Intercept)  8.28391    0.87438   9.474 0.00000000000144 ***
## dist         0.16557    0.01749   9.464 0.00000000000149 ***
## [...]

但我想得到的是

mod <- lm(speed ~ dist, data = cars)
summary(mod)
## [...]
## Coefficients:
##             Estimate Std. Error t value         Pr(>|t|)    
## (Intercept)  8.28391    0.87438   9.474 0.00000000000144 ***
## dist         0.16557    0.01749   9.464 0.00000000000149 ***
## [...]

查看summary(mod)的不同格式。

Answer 1

这是我的问题的解决方案

---
output: html_document
---

```{r, echo=FALSE}
library(knitr)
# the default output hook
hook_output <- knit_hooks$get('output')
knit_hooks$set(output = function(x, options) {
  if (!is.null(n <- options$out.lines)) {
    n <- as.numeric(n)
    x <- unlist(stringr::str_split(x, "\n"))
    nx <- length(x) 
    x <- x[pmin(n,nx)]
    if(min(n) > 1)  
      x <- c(paste(options$comment, "[...]"), x)
    if(max(n) < nx) 
      x <- c(x, paste(options$comment, "[...]"))
    x <- paste(c(x, "\n"), collapse = "\n")
  }
  hook_output(x, options)
    })
```

```{r collapse=TRUE, out.lines = 9:12}
mod <- lm(speed ~ dist, data = cars)
summary(mod)
```

```{r collapse=TRUE, out.lines = 1:3}
summary(mod)
```

```{r collapse=TRUE, out.lines = 17:18}
summary(mod)
```

```{r collapse=TRUE, out.lines = 1:20}
summary(mod)
```

Answer 2

knitr example 052 应该给你一个基本的想法：定义output 钩子，你可以以任何你想要的方式操作文本。

knitr::knit_hooks$set(output = function(x, options) {
  # manipulate x here
})