Dynamic Rstudio Code Snippet - r

Question

I tend to use a lot of line breaks in my code like the following:
# Data =========================================================================
Where the entire comment is always 80 characters long (including the hashtag). What I would like to do is write a code snippet for Rstudio that will insert the hashtag, then a space, then allow the user to type out a series of words, then insert another space, and finally fill in a bunch of "=" until the 80 character limit is reached.
I'm not familiar with how snippets work at all so I'm not sure how difficult this is.
I have this much:
snippet lb
# ${1:name}
but I have no idea how to add a dynamic number of "=" signs. Also, lb = linebreak.

Answer 1

You can't do this with snippets, unfortunately; a snippet is a text template that contains fixed text with slots for user-inserted text.
There is a command built into RStudio to do something very similar, however; from the Code menu, choose Insert Section (or Ctrl+Shift+R). This will do exactly what you're describing, with two small differences:
The line will extend to 5 characters before the print margin (you can adjust the print margin in Tools -> Global Options -> Code.
The line is composed of - rather than = characters.
One advantage to sections marked in this way is that you can use them to fold and navigate inside the file (look at the editor status bar after adding one).

Answer 2

You can use the rstudioapi (which can return column position) inside the snippet to get something like what you want.
Below is a snippet I use called endhead. I use it by commenting my header title and then applying the snippet, eg:
# Section name endhead
which results in:
# Section name -----------------------------------------------------------------
snippet endhead
`r paste0(rep.int("-", 88 - rstudioapi::primary_selection(rstudioapi::getActiveDocumentContext())$range$start[2]), collapse = "")`

Answer 3

You can write a snippet to manipulate text (somewhat). I wrote the snippet below to do something similar to what you want to do. I'm still ironing out the issues (just asked this question).
snippet comm
`r paste0(
"#######################################><###################\n## ",
date(),
" -------------------------------\n## ",
eval(
paste0(
gsub(
".{1,51}\\s?\\K\\b",
"\n## ",
gsub("\\.", " ", paste0(text)),
perl = T
)
)
),
"###################################><###################\n"
)`
I think if you write an R code snippet using an anonymous function that accepts text input via $$, counts the nchar in the text, calculates the number of -'s needed at the end, and then uses eval(paste0()) to insert the comment you should be able to make it work. I'll post a comment or answer here if I figure it out. Please do the same on my question if you get it to work. Thanks. (P.S. Go Badgers!)

Answer 4

Inspired by nick's answer above I designed two snippets that allow the user to choose what level section to insert.
The first will fill-in the rest of the line with #, =, or -.
snippet end
`r strrep(ifelse(substr("$$", 1, 1) %in% c("-", "="), substr("$$", 1, 1), "#"), 84 - rstudioapi::primary_selection(rstudioapi::getActiveDocumentContext())$range$start[2])`
Just specify the character you want to use after end (will default to # if nothing or any other character is given). For example:
## Level 1 Header end<shift+tab>
## Level 2 Header end=<shift+tab>
## Level 3 Header end-<shift+tab>
end<shift+tab>
end=<shift+tab>
end-<shift+tab>
Produces the following lines:
## Level 1 Header ##############################################################
## Level 2 Header =============================================================
## Level 3 Header -------------------------------------------------------------
################################################################################
===============================================================================
-------------------------------------------------------------------------------

Answer 5

Similarly to what Josh was suggesting, the following snippet uses th $$ notation to pass the text following the snippet as described here.
snippet !
`r paste("##", substr("$$", 4, nchar("$$")), strrep(substr("$$", 2, 2), 79-nchar("$$")))`
Again this allows user to select the section level (#, =, or -). The first character after !# should be the header level character you want followed by a space and the header text. For example:
!## Level 1 Header<shift+tab>
!#= Level 2 Header<shift+tab>
!#- Level 3 Header<shift+tab>
Produces the following lines:
## Level 1 Header ##############################################################
## Level 2 Header ==============================================================
## Level 3 Header --------------------------------------------------------------
I prefer the end snippet above because it is more robust and only allows the characters #, =, or - to be inserted where as ! will allow anything, but it is shorter and, I think, easier to understand than calls to the rstudioapi.
!loon<shift+tab>
## n ooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooo