R: Hooks for code chunk options

opts_hooks {knitr} | R Documentation

## Hooks for code chunk options

### Description

Like `knit_hooks`, this object can be used to set hook functions to manipulate chunk options.

### Usage

    opts_hooks

### Format

An object of class `list` of length 4.

### Details

For every code chunk, if the chunk option named, say, `FOO`, is not `NULL`, and a hook function with the same name has been set via `opts_hooks$set(FOO = function(options) { options })` (you can manipuate the `options` argument in the function and return it), the hook function will be called to update the chunk options.

### References

https://yihui.name/knitr/hooks/

### Examples

    # make sure the figure width is no smaller than fig.height
    opts_hooks$set(fig.width = function(options) {
        if (options$fig.width < options$fig.height) {
            options$fig.width = options$fig.height
        }
        options
    })
    # remove all hooks
    opts_hooks$restore()

[Package knitr version 1.16 Index]