External package guessing output format

[zeehio]

Thanks for your time and effort on both rmarkdown and knitr.

Let's say I have a package with a function that returns an S3 object:

new_myclass <- function() {
  return(structure(list(a=1, b=2), class = "myclass"))
}

I also have two functions that take a myclass object and return respectively a HTML representation and a LaTeX representation of the object.

myclass2html <- function(obj) { return("<p>MyClass object</p>")}
myclass2latex <- function(obj) { return("\begin{em}MyClass\end{em} object $x$")}

What functions/methods should I define to provide consistent and transparent knitr and rmarkdown support? I would like to support both .Rmd files and .R files with a header like:

#'---
#' title: My document
#' output: pdf_output
#'---

So far my approach is:

#' @importFrom rmarkdown metadata
#' @importFrom knitr opts_knit
guess_output_format <- function() {
  rmd_output <- tryCatch({rmarkdown::metadata$output},
                         error = function(e) {NULL})
  if (is.null(rmd_output)) {
    rmd_output = ""
  }
  if (is.list(rmd_output)) {
    rmd_output <- names(rmd_output)[1]
  }
  if (rmd_output == "pdf_document") {
    return("latex")
  } else if (rmd_output %in% c("html_document", "html_vignette")) {
    return("html")
  } else if (rmd_output != "") {
    return("")
  }
  # No rmarkdown, let's try with knitr:
  format <- knitr::opts_knit$get("out.format")
  if (format %in% c("html", "markdown")) {
    return("html")
  } else if (format %in% c("latex")) {
    return("latex")
  } else {
    return("")
  }
}

My main issue is that there may be two variables rmarkdown::metadata$output and knitr::opts_knit$get("out.format") that may or may not be defined (depending on whether or not rmarkdown is being used). I find this confusing.

• What is the right way to know the output format?
• Is there a get_output_format function that tells me the output format?

To put the question in context, I am working on the condformat package that allows to visualize DataFrames with conditional formatting rules.

This question has been asked also in stackoverflow without answer in several days.

Thanks for any piece of advice

[jjallaire]

We define some knitr options that give you the pandoc to and from formats:

https://github.com/rstudio/rmarkdown/blob/master/R/render.R#L246-L252

Note that getting the name of the output format isn't that helpful as
there could be dozens of output formats you'd need to write code to
determine whether they are HTML or PDF. I'd say you should check the
output.to and look for "latex" or "beamer" to discover PDF output and then
assume HTML for everything else (i.e. don't try to emit RTF, ODF, MS Word,
markdown, etc.).

On Tue, Mar 22, 2016 at 5:56 AM, Sergio Oller [email protected]
wrote:

Thanks for your time and effort on both rmarkdown and knitr.

Let's say I have a package with a function that returns an S3 object:

new_myclass <- function() {
return(structure(list(a=1, b=2), class = "myclass"))
}

I also have two functions that take a myclass object and return
respectively a HTML representation and a LaTeX representation of the object.

myclass2html <- function(obj) { return("

MyClass object

")}myclass2latex <- function(obj) { return("\begin{em}MyClass\end{em} object $x$")}

What functions/methods should I define to provide consistent and
transparent knitr and rmarkdown support? I would like to support both .Rmd
files and .R files with a header like:

#'---#' title: My document#' output: pdf_output#'---

So far my approach is:

#' @importFrom rmarkdown metadata#' @importFrom knitr opts_knitguess_output_format <- function() {
rmd_output <- tryCatch({rmarkdown::metadata$output},
error = function(e) {NULL})
if (is.null(rmd_output)) {
rmd_output = ""
}
if (is.list(rmd_output)) {
rmd_output <- names(rmd_output)[1]
}
if (rmd_output == "pdf_document") {
return("latex")
} else if (rmd_output %in% c("html_document", "html_vignette")) {
return("html")
} else if (rmd_output != "") {
return("")
}

No rmarkdown, let's try with knitr:

format <- knitr::opts_knit$get("out.format")
if (format %in% c("html", "markdown")) {
return("html")
} else if (format %in% c("latex")) {
return("latex")
} else {
return("")
}
}

My main issue is that there may be two variables
rmarkdown::metadata$output and knitr::opts_knit$get("out.format") that
may or may not be defined (depending on whether or not rmarkdown is being
used). I find this confusing.

• What is the right way to know the output format?
• Is there a get_output_format function that tells me the output
  format?

To put the question in context, I am working on the condformat
http://www.sergioller.com/2016-03-10-condformat-release.md package that
allows to visualize DataFrames with conditional formatting rules.

This question has been asked also in stackoverflow
http://stackoverflow.com/questions/36044610/print-custom-object-in-rmarkdown-and-knitr-pdf-and-html
without answer in several days.

Thanks for any piece of advice

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#649

[zeehio]

Thanks @jjallaire, rmarkdown.pandoc.to makes things easier to me.

To make it better to future developers, would you accept a pull request to export knitr:::is_html_output, knitr:::is_latex_output, knitr::escape_html and knitr:::escape_latex? (or at least the first two?)

Otherwise I am happy enough with my approach:

• If format is either "latex" or "beamer" then: output to LaTeX
• If format is either "html" or starts with "markdown" (many markdown flavours!) then: output to HTML
• Else: Use a generic output (I forgot to mention I have one)

#' @importFrom rmarkdown metadata
#' @importFrom knitr opts_knit
guess_output_format <- function() {
  outfmt <- knitr::opts_knit$get("rmarkdown.pandoc.to")
  if (is.null(outfmt)) {
    outfmt <- knitr::opts_knit$get("out.format")
  }
  if (is.null(outfmt)) {
    return("") # not in knitr
  }
  if (outfmt %in% c("latex", "beamer")) {
    return("latex")
  } else if (outfmt == "html" || substr(outfmt, 1, nchar("markdown")) == "markdown") {
    return("html")
  } else {
    return("unsupported") # uses a generic fallback
  }
}

Here is in its context

Thanks!

[jjallaire]

@yihui, maybe we could even have a function like this:

knitr::current_output_type()

Which returns either "latex", "html", "markdown", or "unknown"

On Tue, Mar 22, 2016 at 8:41 AM, Sergio Oller [email protected]
wrote:

Thanks @jjallaire https://github.com/jjallaire, rmarkdown.pandoc.to
makes things easier to me.

To make it better to future developers, would you accept a pull request to
export knitr:::is_html_output, knitr:::is_latex_output, knitr::escape_html
and knitr:::escape_latex? (or at least the first two?)

Otherwise I am happy enough with my approach:

• If format is either "latex" or "beamer" then: output to LaTeX
• If format is either "html" or starts with "markdown" (many markdown
  flavours!) then: output to HTML
• Else: Use a generic output (I forgot to mention I have one)

#' @importFrom rmarkdown metadata#' @importFrom knitr opts_knitguess_output_format <- function() {
outfmt <- knitr::opts_knit$get("rmarkdown.pandoc.to")
if (is.null(outfmt)) {
outfmt <- knitr::opts_knit$get("out.format")
}
if (is.null(outfmt)) {
return("") # not in knitr
}
if (outfmt %in% c("latex", "beamer")) {
return("latex")
} else if (outfmt == "html" || substr(outfmt, 1, nchar("markdown")) == "markdown") {
return("html")
} else {
return("unsupported") # uses a generic fallback
}
}

Here is in its context
https://github.com/zeehio/condformat/blob/master/R/condformat_render.R#L72

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#649 (comment)

[yihui]

Okay, I'll consider exporting some of these functions from knitr.

[yihui]

I have exported is_latex_output and is_html_output in the dev version of knitr.

[hughjonesd]

Actually, it would be useful for package authors to get the name of the current output format. For example, bookdown uses a special reference scheme for tables. I currently detect this by looking at
rmarkdown::default_output_format(knitr::current_input()). That can be wrong if the default format is not what is being knitted. Could this be reopened?

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