knitr::opts_chunk$set(comment = "", echo = FALSE) library(bannerCommenter)
This tiny package is for the convenience of R
script authors
who wish to document their code with the occasional block of clearly
marked comment lines in order to make the code more easily navigable
by others, or even by the same author at some later date.
A common practice is to use comment lines enclosed in some kind of band, or box of display characters. We call such a block of comments a banner comment, and by using them sparingly and judiciously code can be made much easier to navigate visually and hence to maintain.
Examples might include blocks such as the following to initiate a major code section:
section("Section 1", "Data input and initialization")
Subsections might be flagged by less prominent comments such as one like this
boxup("Primary data input", bandChar = "-", center = TRUE)
or a more minor one like
open_box("Some minor glitches in the data\nneed special treatment here", bandChar = ".", snug = TRUE)
Banner comments look much better if there is a consistent formatting throughout the script so that sections and sub-sections can be readily identified. This is quite easy to do, but to do it properly can take some editing and drafting time.
The simple tool we offer here aims to make the formatting tasks essentially no more work than typing the text itself. It presumes that while the R script is being drafted there will be a console window open as well, but this is almost de rigeur these days.
The package bannerCommenter
provides a single main function,
banner
, along with a few helpers.
To make a banner such as the first one above you could simply type the text into the console window via a call to the main function:
library(bannerCommenter) banner("Section 1:", "Data input and initialization", emph = TRUE)
This provides a formatted comment that can be copy-and-pasted into the
script. However, if the operating system allows it, as well as
displaying the comment in the console window the result is also
copied onto a clipboard
file or pipe, so the "copy" part of the
copy-and-paste should not be required.
Two other conveniences are also provided.
Since this is likely to be a common form of banner comment, a
simple front-end function section()
is provided which simply
called banner(..., emph = TRUE)
, that is with the emph
argument
having a different default value.
Rather than typing strings with quote delimiters separated by
commas, if the function is called with no string arguments,
the strings are read from the console, line by line, with prompts
issued as with the scan
function. An empty line indicates
the text input complete.
The process is particularly simple when working in RStudio
. The
script will be composed in the Source
pane. When a banner comment
is desired, the process is:
Place the cursor at the beginning of the line where you want the comment to appear.
Press Ctrl-1
to move the focus to the console pane.
Type banner()
or one of the alternatives.
Enter the text of your comment, one line per line, terminated by a blank line.
Press Ctrl-2
to shift the focus back to the Source
pane, followed by
either Ctrl-v
or Ctrl-y
(both seem to work!) to transfer the complete
comment to the script.
If for some reason you make a slip and lose the clipboard contents, the full comment remains available in the console window for copy-and-paste.
An example, again with the same banner comment, is as follows
> section() 1: Section 1 2: Data input and initialization 3: ########################################################################### ########################################################################### ### ### ### SECTION 1 ### ### DATA INPUT AND INITIALIZATION ### ### ### ########################################################################### ########################################################################### >
At this point the user should be able to paste the banner comment into the script in the usual way. If the automatic clipboard facility is not available the band displayed in the console window, essentially for checking, can easily be used for manual copy-and-paste.
In a series of similar comment banners the function would normally be invoked by command line recall making only the typing of the text itself necessary.
At first sight banner
seems to have a bewildering number of arguments, but most have sensible
defaults and there are four front-end functions like section
that handle simple
special cases where the default values are slightly different.
The full list of arguments to banner
and their default values are listed in the
table below. Note that some argument defaults refer to the values of other arguments.
txt <- structure(c("`x, ...`", "", "`emph`", "`snug`", "`upper`", "`centre`", "`leftSideHashes`", "`rightSideHashes`", "`minHashes`", "`numLines`", "`bandChar`", "`center`", "`fold`", "`maxChar`", "One or more strings, which may be missing.", "(Single strings may be further broken by '`\\n`'.)", "Do you want emphasis, i.e. a bigger, bolder banner?", "Do you want any box to be close fitting?", "Do you want the text to be in upper case?", "Do you want the text lines to be centred?", "How many hash characters to the left?", "How many hash characters to the right", "How long do you want the bands (at least)?", "How many lines above and below do you want?", "What character do you want to use for the bands?", "Alternative (foreign) spelling of '`centre`'", "Do you want `banner` to find suitable line breaks?", "Maximum number of characters in any one line, (if `fold`).", "`<none>`", "", "`FALSE`", "`FALSE`", "`emph`", "`!fold`", "`2 + emph`", "`leftSideHashes`", "`(!snug) * (65 + 10 * emph)`", "`1 + emph`", "`\"#\"`", "`centre`", "`FALSE`", "75"), .Dim = c(14L, 3L), .Dimnames = list(NULL, c("Argument", "Meaning", "Default"))) knitr::kable(txt)
As well as section
there are three other front-end functions that
simply act as a call to banner
with different default values for
some of the arguments. Rather than describe them in detail it
suffices simply to provide a few example, beginning with the primary
function itself.
txt <- "This is the text of a comment" banner(txt) ## default heavy style banner(txt, centre = TRUE, bandChar = "-") boxup(txt, snug = TRUE, bandChar = "=") open_box(txt, bandChar = ":") block(paste("This is a chatty comment. Entering it this way just", "saves a tiny bit of typing but it can be useful if", "you need multiple initial hash marks, as you may when", "using editors in RStudio or Emacs/ESS, for example.", "Or if you want the lines folded to make things more compact.", collapse = " "), fold = TRUE) boxup("") ## short lines of uniform length, for use as a separator section("") ## heavier, longer double lines to separate bigger things
In some editing systems, where a comment has only white space before it on a
single line, the number of leading comment characters is significant. It affects
how the line is changed under automatic reformatting. For example, Emacs/ESS
adopts this convention by default:
A line with a single leading comment character, only, is aligned so that it begins near the middle of the line. (I have no explanation as to why!)
A line with two leading comment characters, only, is aligned as if it were an active code line. This is often useful.
A line with three or more leading comment characters is aligned so that it begins in the first column and so occupies the whole line.
Some commentators recommend using a single leading comment character for all comments,
and RStudio
, for example, facilitates this choice. However if the same code is handled
by Emacs/Ess
the comments are liable to be right shifted to start in the middle of the
line (unless the default is changed, of course, which is not initially very clear).
This may be useful to keep in mind when two or more systems may be used to maintain
the same R
scripts.
A helper function used in this package may be useful in its own right.
The function copy_to_clipboard
allows text strings to be copied to a
clipboard file (or pipe) in a reasonably cross platform way, at least
for Linux
, Windows
and Mac OS
.
A call such as
copy_to_clipboard(txt)
will return txt
invisibly, but will have the side effect of
transferring any strings in the txt
object to a clipboard device.
In effect it behaves like a print
method, but with the "printing"
going on to a clipboard device rather than on to stdout
.
To work on Linux
the system command xclip
has to be installed and
visible on the PATH
and on Mac OS
the system command pbcopy
has
similarly to be installed and visible. On Windows
it should work
universally.
Note that this is not a file or pipe connection in itself, but a function which transfers strings to an appropriate clipboard device. Thus, for example, to write a short data frame onto a clipboard device in a way that works across the three platforms, you may need to do something like the following:
library(dplyr) mtcarsText <- datasets::mtcars %>% capture.output(write.table(.)) %>% copy_to_clipboard(sep = "\n")
At this point mrcarsText
is a character string vector with the lines
of datasets::mtcars
as its elements, and the information would be
available on the clipboard for a paste operation.
Use sparingly and judiciously. Most comments will simply be done by
typing the #
character and proceeding. They will usually not
require fancy banners. A potential danger of providing this simple
facility is that some authors may be tempted to overdo their script
decoration. Comments are important, but excessive fancy comments will
detract from the aesthetics and waste a lot of otherwise productive
coding time.
People who find the package useful but would like to suggest other tweaks or front-ends are welcome to contact the author at the email address given in the package itself.
Any scripts or data that you put into this service are public.
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