Allow numeric values for fig.keep to index plots

[ClaudiusL]

This is a feature request based on this question on SO.

So far, fig.keep accepts only 'high', 'none', 'first', 'last' (and, implicitly, 'all') . Would it be possible to extend the functionality in a way similar to echo, such that fig.keep = c(1, 3) keeps the first and the third plot?

One potential drawback is that fig.keep = c(1, 3) cannot be combined with fig.kepp = 'high'. Therefore, the indices would implicitly always refer to low-level plots. (The same already applies to fig.keep = 'first').

I think the implementation could be quite simple: In block.R, line 222, an additional if clause could be added:

if (keep %in% c('first', 'last')) {
  res = res[-(if (keep == 'last') head else tail)(which(figs), -1L)]
} else {
   if (is.numeric(keep)) { #new 
     res = res[which(figs)[keep]]
    }
  # merge low-level plotting changes
  if (keep == 'high') res = merge_low_plot(res, figs)
}

However, I am not entirely sure about the contents of res and figs, so my suggested code might be wrong.

[yihui]

That looks okay to me. Could you submit a pull request? Thanks!

[ClaudiusL]

I also proposed an update for http://yihui.name/knitr/options/. Should this be a separate pull request? (Not sure about the correct workflow for this.)

[yihui]

Yes, the docs are in the gh-pages branch. Please submit a separate PR for that. Thanks!

[ClaudiusL]

Ok. Slowly I'm getting used to how this works … ;)

[github-actions]

This old thread has been automatically locked. If you think you have found something related to this, please open a new issue by following the issue guide (https://yihui.org/issue/), and link to this old issue if necessary.