In pvrqualitasag/AtdaAsrProjectTestFinalDocu:

Three arguments in chunk hooks

A chunk hook has three arguments: before, options and envir. We show how they work through some simple examples.

The before argument

It is a logical argument: before == TRUE executes code before a chunk.

library(knitr)
knit_hooks$set(foo1 = function(before, options, envir) {
  if (before) {
    '_I appear before a chunk!_\n\n'
  } else {
    '\n\n_I am after a chunk..._'
  }
})

Test the foo1 hook:

1+1

The options argument

It contains all the chunk options (include global options) for the current chunk.

knit_hooks$set(foo2 = function(before, options, envir) {
  if (!before) {
    z = capture.output(str(options[c('eval', 'dev', 'results', 'bar1', 'bar2', 'bar3','label')]))
    z = paste('    ', z, sep = '', collapse = '\n')
    paste('Some chunk options in the above chunk are:\n\n', z, sep = '')
  }
})

Test the foo2 hook:

1+1

The envir argument

It is the environment of the current chunk.

knit_hooks$set(foo3 = function(before, options, envir) {
  if (!before) {
    paste('Objects available in the above chunk:',
          paste('`', ls(envir), '`', sep = '', collapse = ', '))
  }
})

Test the foo3 hook:

x2=1+1; y3=rnorm(10)

Another example:

knit_hooks$set(foo4 = function(before, options, envir) {
  if (!before && exists('z5', envir = envir)) {
    sprintf('**Ha! I see z5 = %.3f!**', envir$z5)
  }
})

Test foo4:

pi

This above chunk is quiet because z5 does not exist yet.

z5=2*pi

Own example

We want to use chunk-hooks to convert graphics from a given format, like LibreOffice-Draw into pdf or png which can be included in documents.

knit_hooks$set(conv.odg = function(before, options, envir) {
  if (is.null(options$label))
    stop(" *** ERROR: chunk must be labelled\n")
  if (is.null(options$odg.path)){
    odg.path <- "odg"
  } else {
    odg.path <- options$odg.path
  }
  odg.fname <- paste(options$label, "odg", sep = ".")
  odg.fig.src  <- file.path(odg.path, odg.fname)
  trg.fig <- paste(options$label, "pdf", sep = ".")
  if (before) {
    if (!file.exists(odg.fig.src))
      rmddochelper::create_odg_graphic(psGraphicName = odg.fname, psGraphicPath = odg.path)
    if (!file.exists(trg.fig) | !options$odg.graph.cache)
      rmddochelper:::convertLibOToGraphic(psLibOFile = odg.fname, psOutFormat = "pdf", psLibODir = odg.path)
  }
})

Now we create a chunk that includes a figure

knitr::include_graphics(path = "FigInclude.pdf")

This is the first line after the figure inclusion.

Sys.time()
sessionInfo()

pvrqualitasag/AtdaAsrProjectTestFinalDocu documentation built on May 26, 2019, 11:34 a.m.