knit_ex: Knitr Extensions

Description

knit_ex is a utility function for running small knitr examples, e.g., to illustrate functionalities or issues.

hook_backspace is a chunk hook that enables the use of backspace characters in the output (e.g., as used in progress bars), and still obtain a final output as in the console.

Usage

knit_ex(x, ..., quiet = TRUE, open = FALSE)
hook_try(before, options, envir)
hook_backspace()
hook_toggle()

Arguments

text to knit as a character vector

...

arguments passed to knit2html or knit

quiet

logical that indicates if knitting should be quiet (no progress bars etc..).

open

logical, only used when x is in .Rmd format, that indicates if the generated document result should be open in a browse, instead of being printed on screen. Not that a browser will not open in non-interactive sessions, and the result will be returned invisibly.

before

logical that indicates when the hook is being called: before or after the chunk is processed.

options

list of current knitr chunk options

envir

environment where the chunk is evaluated

Value

knit_ex returns the generated code, although invisibly when open=TRUE.

Functions

hook_try: is a knitr hook to enable showing error messages thrown by try. The function is not meant to be called directly, but only registered using knitr::knit_hooks (see details on this dedicated man page).

This simply defines a function try in envir that prints the error message if any, and is called instead of base try.
hook_toggle: is a chunk hook that adds clickable elements to toggle indvidual code chunks in HTML documents generated from .Rmd files.

Examples

Run this code

# NOT RUN {
library(knitr)
knit_ex("1 + 1")


library(knitr)

# standard error message is caught
knit_ex("stop('ah ah')")

# with try the error is output on stderr but not caughted by knitr
knit_ex("try( stop('ah ah') )")

# no message caught
knit_ex("
^^^{r, include = FALSE}
knit_hooks$set(try = pkgmaker::hook_try)
^^^

^^^{r, try=TRUE}
try( stop('ah ah') )
^^^")


# Correctly formatting backspaces in chunk outputs
tmp <- tempfile(fileext = '.Rmd')
cat(file = tmp, "
^^^{r, include = FALSE}
library(knitr)
knit_hooks$set(backspace = pkgmaker::hook_backspace())
^^^
Default knitr does not handle backspace and adds a special character:
^^^{r}
cat('abc\bd')
^^^

Using the hook backspace solves the issue:
^^^{r, backspace=TRUE}
cat('abc\bd')
^^^
")

# knit
out <- knitr::knit2html(tmp, fragment.only = TRUE)
# look at output
# }
# NOT RUN {
  browseURL(out)
  edit( file = out)
# }
# NOT RUN {
# cleanup
out_files <- list.files(dirname(out), full.names = TRUE,
                         pattern = paste0("^", tools::file_path_sans_ext(out))) 
unlink(c(tmp, out_files))



knit_ex("

Declare chunk hook:
^^^{r, setup}
library(knitr)
knit_hooks$set(toggle = hook_toggle())
^^^

The R code of this chunk can be toggled on/off, and starts visible:
^^^{r, toggle=TRUE}
print(1:10)
^^^
The R code of this chunk can be toggled on/off, and starts hidden:
^^^{r, toggle=FALSE}
print(1:10)
^^^

This is a plain chunk that cannot be toggled on/off:
^^^{r}
print(1:10)
^^^

Now all chunks can be toggled and start visible:
^^^{r, toggle_all}
opts_chunk$set(toggle = TRUE)
^^^

^^^{r}
sample(5)
^^^

To diable the toggle link, one can pass anything except TRUE/FALSE:
^^^{r, toggle = NA}
sample(5)
^^^

", open = TRUE)

# }

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