How to set knitr chunk output width on a per chunk basis?

Question

My question(s): Does knitr have an option that allows one to set R's `width` option on a per chunk basis? If not, is there a good reason (i.e. one rooted in some fundamental limitation of the knitr model) that it does not? What I've tried: To show what I'm wishing for, here is a hand-rolled hook function that does basically what I want. (I don't really like it though, (a) because it is ugly, relying on assignment of the variable `.width` into the global environment, and (b) because it's not available "out of the box" as a supplied option like `fig.width`, `out.width`, et al.) ``` \documentclass[preview=true,width=3mm]{standalone} \begin{document} <>= options(width=60) knit_hooks$set(width = function(before, options, envir) { if(before) { .width <<- options(width=options$width) ## Set width and save 'old' value } else { options(.width)} ## Restore width's 'old' value }) @ First chunk uses default width <>= c("aaaaa", "bbbbb", "ccccc", "ddddd", "eee…

Accepted Answer

Though not a solution to the overall question, your first complaint with your code is that it gums up the global environment with your `.width` variable. This can be resolved using `local()` as a closure mechanism, encapsulating your variable so that you get no collisions in global var space.

So, if you replace your `knit_hooks$set` call with:

```
knit_hooks$set(width=local({
    .width <- 0
    function(before, options, envir) {
        if (before) .width <<- options(width=options$width)
        else options(.width)
    }
}))
```

it produces the same results without the problem of forcing `.width` into the global environment. The rest of your code above works as before with identical output.

More can be read at `help(local)`, in Advanced R Programming (Hadley Wickham), and there are several examples of it in the wild, such as @JeroenOoms' OpenCPU.

How to set knitr chunk output width on a per chunk basis?

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