In R, how do I match markdown list - regex

Question

I'm trying to match the following ordered and unordered lists and extract the bullet/list point.
library(stringr)
examples <- c(
"* Bullet 1\n* Bullet 2\n* Bullet 3",
"1. Bullet 1\n2. Bullet 2\n3. Bullet 3",
"* This is a test 1\n* This is a test with some *formatting*\n* This is a test with different _formatting_"
)
What I would like to do is:
Recognize that it's a list programatically
Parse each into just the text of the list item
The result would be
some_str_fun(example,pattern) # or multiples
"Bullet 1" "Bullet 2" "Bullet 3"
"Bullet 1" "Bullet 2" "Bullet 3"
"This is a test 1" "This is a test with some *formatting*"
"This is a test with different _formatting_"
I've been playing with the following patterns, and str_extract/match but can't seem to find something completely functional
[*]+\\s(.*?)[\n]* # for * Bullet X\n
[1-9]+[.]\\s(.*?)[\n]* # for 1. Bullet X\n
I've tried a bunch of different iterations on these patters but can't quite seem to get what I'm looking for.

Answer 1

You can use strapply from the gsubfn package to match the entire pattern.
library(gsubfn)
examples <- c(
"* Bullet 1\n* Bullet 2\n* Bullet 3",
"1. Bullet 1\n2. Bullet 2\n3. Bullet 3",
"* This is a test 1\n* This is a test with some *formatting*\n* This is a test with different _formatting_"
)
strapply(examples, '(?:\\*|\\d+\\.) *([^\n]+)', c, simplify = c)
# [1] "Bullet 1"
# [2] "Bullet 2"
# [3] "Bullet 3"
# [4] "Bullet 1"
# [5] "Bullet 2"
# [6] "Bullet 3"
# [7] "This is a test 1"
# [8] "This is a test with some *formatting*"
# [9] "This is a test with different _formatting_"

Answer 2

This is a bit of a different approach, but if you render the markdown to HTML you can use some existing extraction methods to do what you want:
library(stringr)
examples <- c(
"* Bullet 1\n* Bullet 2\n* Bullet 3",
"1. Bullet 1\n2. Bullet 2\n3. Bullet 3",
"* This is a test 1\n* This is a test with some *formatting*\n* This is a test with different _formatting_"
)
extract_md_list <- function(md_text) {
require(rvest)
require(rmarkdown)
fil_md <- tempfile()
fil_html <- tempfile()
writeLines(md_text, con=fil_md)
render(fil_md, output_format="html_document", output_file=fil_html, quiet=TRUE)
pg <- html(fil_html)
ret <- html_nodes(pg, "li") %>% html_text()
# cleanup
unlink(fil_md)
unlink(fil_html)
return(ret)
}
extract_md_list(examples)
## [1] "Bullet 1"
## [2] "Bullet 2"
## [3] "Bullet 3"
## [4] "Bullet 1"
## [5] "Bullet 2"
## [6] "Bullet 3"
## [7] "This is a test 1"
## [8] "This is a test with some formatting"
## [9] "This is a test with different formatting"

Answer 3

Here is another option. You can wrap in unlist if desired:
str_extract_all(examples, "[^*1-9\n ]\\w+( ?[\\w*]+)*")
# or
#str_extract_all(examples, "[^*1-9\n ]\\w+( ?[a-zA-Z0-9_*]+)*")
#[[1]]
#[1] "Bullet 1" "Bullet 2" "Bullet 3"
#
#[[2]]
#[1] "Bullet 1" "Bullet 2" "Bullet 3"
#
#[[3]]
#[1] "This is a test 1"
#[2] "This is a test with some *formatting*"
#[3] "This is a test with different _formatting_"
There are several other options, particularly if you're not concerned about getting it all in a single regex or single line of code. Here's one more approach. The regex is simpler, but you end up with "", which requires the additional line:
splits <- unlist(str_split(examples, "\n|\\d+\\. |\\* "))
splits[splits != ""]
#[1] "Bullet 1"
#[2] "Bullet 2"
#[3] "Bullet 3"
#[4] "Bullet 1"
#[5] "Bullet 2"
#[6] "Bullet 3"
#[7] "This is a test 1"
#[8] "This is a test with some *formatting*"
#[9] "This is a test with different _formatting_"