在 knitr 中缩写长 R 输出

Question

I remember that I've seen a hook in knitr to abbreviate R output. But I forgot how to accomplish this task. How can I show first few lines and last few lines of R output connected with ellipses (...) .

   \documentclass{article}
    \begin{document}

    << Test >>=
    1:1000
    @
    \end{document}

I found this link but it does not work for me.

Edited

@kohske solution is excellent and works fine if there is only one output. Need more generalization for such Chunk.

<< label=Test, results = "hold" >>=
1:1000
args(lm)
@ 

Answer 1

Is this what you want?

\documentclass{article}
\begin{document}

<<include=FALSE>>=
library(knitr)
oh <- knit_hooks$get("output")
knit_hooks$set(output = function(x, options) {
  ret <- strsplit(x, "\n")[[1]]
  ret <- paste0(ret[1], "\n...\n", ret[length(ret)])
  oh(ret, options)
})
@


<< Test>>=
1:1000
@
\end{document}

UPDATE

knit_hooks$set(output = function(x, options) {
  ret <- strsplit(x, "\n")[[1]]
  ret <- if (length(ret) > 2)
    paste0(ret[1], "\n...\n", ret[length(ret)])
  else
    ret
  oh(ret, options)
})