问题
I have seen both angled brackets:
<<>>=
...
@
and back ticks:
```{}
...
```
used to indicate 'chunks' in the knitr documentation. What is the difference between these two?
For example, can I replace the following block of code from the documentation:
<<my-label, eval=TRUE, dev='png'>>=
set.seed(1213) # for reproducibility
x = cumsum(rnorm(100))
mean(x) # mean of x
plot(x, type = 'l') # Brownian motion
@
with:
```{r my-label}
set.seed(1213) # for reproducibility
x = cumsum(rnorm(100))
mean(x) # mean of x
plot(x, type = 'l') # Brownian motion
```
回答1:
The backtick syntax is used in Rmarkdown documents (Markdown mixed with R code: usually stored as file extension .rmd), while the angle-bracket syntax is used in documents that mix LaTeX with R code (usually stored as .Rnw). I'm not sure what to call the latter; they used to be "Sweave documents", but the Sweave package has been largely superseded by the knitr package. However, knitr (and the rmarkdown package) can both process both markdown+R and LaTeX+R documents ...
Your suggested substitution of
```{r chunklabel,..options..}
...
```
for
<<chunklabel,..options..>>=
...
@
seems reasonable (and very easy to just try it out!) Of course, you will need to make sure that the knitr/rmarkdown tools you're using know what syntax type you're starting with. knitr::knit seems (based on docs) to guess from the file extension. The docs for rmarkdown::render only talk about .rmd.
The easiest way to figure all this out is probably just to do a few experiments.
回答2:
One difference seems to be when using chunk references to reuse chunks, addressed by this question and the link to the documentation on Reference/Macro, which only makes use of <<>> type chunks. Duplicating the example:
<<chunk1>>=
1 + 1
@
<<chunk2>>=
<<chunk1>>
@
such that the second chunk simply duplicates the code in chunk1.
To convert this into back tick chunks, you seem to need to do:
```{r chunk1}
1 + 1
```
that is, a direct replacement as suggested in my question and Ben Bolker's answer. However, to refer to chunk 1, it seems that angled brackets are still required:
```{r chunk2}```
<<chunk1>>
```
In addition, note that leaving the code as is:
<<chunk2>>=
<<chunk1>>
@
does not work, at least with respect to rmarkdown::render with the file saved with .Rmd extension.
来源：https://stackoverflow.com/questions/41093706/what-is-the-difference-between-knitr-chunks-and-chunks