split a string knowing some of the substrings - r

Question

Say I have the following string and a vector of substrings:
x <- "abc[[+de.f[-[[g"
v <- c("+", "-", "[", "[[")
I would like to split this string by extracting the substrings from my vector and making new substrings from the characters in between, so I would get the following :
res <- c("abc", "[[", "+", "de.f", "[", "-", "[[", "g")
in case of conflicting matches the longer wins (here [[ over [), you can consider there won't be conflicting matches of same length.
Tagging with regex but open to any solution, faster being better.
Please don't make any assumption on the type of character used in any of these strings, apart from the fact they're ASCII. There is no pattern to be inferred if I didn't explicitly mention it.
another example :
x <- "a*bc[[+de.f[-[[g[*+-h-+"
v <- c("+", "-", "[", "[[", "[*", "+-")
res <- c("a*bc", "[[", "+", "de.f", "[", "-", "[[", "g", "[*", "+-", "h", "-", "+")

Answer 1

This almost seems more like a lexing problem than a matching problem. I seem to get decent results with the minilexer package
library(minilexer) #devtools::install_github("coolbutuseless/minilexer")
patterns <- c(
dbracket = "\\[\\[",
bracket = "\\[",
plus = "\\+",
minus = "\\-",
name = "[a-z.]+"
)
x <- "abc[[+de.f[-[[g"
lex(x, patterns)
unname(lex(x, patterns))
# [1] "abc" "[[" "+" "de.f" "[" "-"
# [7] "[[" "g"

Answer 2

Using stringr::str_match_all and Hmisc::escapeRegex :
x <- "abc[[+de.f[-[[g"
v <- c("+", "-", "[", "[[")
tmp <- v[order(-nchar(v))] # sort to have longer first, to match in priority
tmp <- Hmisc::escapeRegex(tmp)
tmp <- paste(tmp,collapse="|") # compile a match string
pattern <- paste0(tmp,"|(.+?)") # add a pattern to match the rest
# extract all matches into a matrix
mat <- stringr::str_match_all(op_chr, pattern)[[1]]
# aggregate where second column is NA
res <- unname(tapply(mat[,1],
cumsum(is.na(mat[,2])) + c(0,cumsum(abs(diff(is.na(mat[,2]))))),
paste, collapse=""))
res
#> [1] "abc" "[[" "+" "de.f" "[" "-" "[[" "g"

Answer 3

A pure regex-based solution will look like
x <- "abc[[+de.f[-[[g"
v <- c("+", "-", "[", "[[")
## Escaping function
regex.escape <- function(string) {
gsub("([][{}()+*^$|\\\\?.])", "\\\\\\1", string)
}
## Sorting by length in the descending order function
sort.by.length.desc <- function (v) v[order( -nchar(v)) ]
pat <- paste(regex.escape(sort.by.length.desc(v)), collapse="|")
pat <- paste0("(?s)", pat, "|(?:(?!", pat, ").)+")
res <- regmatches(x, gregexpr(pat, x, perl=TRUE))
## => [[1]]
## [1] "abc" "[[" "+" "de.f" "[" "-" "[[" "g"
See this R demo online. The PCRE regex here is
(?s)\[\[|\+|-|\[|(?:(?!\[\[|\+|-|\[).)+
See the regex demo and the Regulex graph:
Details
(?s) - a DOTALL modifier that makes . match any char including newlines
\[\[ - [[ substring (escaped with regex.escape)
| - or
\+ - a +
|- - or a - (no need to escape - as it is not inside a character class)
|\[ - or [
| - or
(?:(?!\[\[|\+|-|\[).)+ - a tempered greedy token that matches any char (.), 1 or more repetitions as many as possible (+ at the end), that does not start a a [[, +, - or [ character sequences (learn more about tempered greedy token).
You may also consider a less "regex intensive" solution with a TRE regex:
x <- "abc[[+de.f[-[[g"
v <- c("+", "-", "[", "[[")
## Escaping function
regex.escape <- function(string) {
gsub("([][{}()+*^$|\\\\?.])", "\\\\\\1", string)
}
## Sorting by length in the descending order function
sort.by.length.desc <- function (v) v[order( -nchar(v)) ]
## Interleaving function
riffle3 <- function(a, b) {
mlab <- min(length(a), length(b))
seqmlab <- seq(length=mlab)
c(rbind(a[seqmlab], b[seqmlab]), a[-seqmlab], b[-seqmlab])
}
pat <- paste(regex.escape(sort.by.length.desc(v)), collapse="|")
res <- riffle3(regmatches(x, gregexpr(pat, x), invert=TRUE)[[1]], regmatches(x, gregexpr(pat, x))[[1]])
res <- res[res != ""]
## => [1] "abc" "[[" "+" "de.f" "[" "-" "[[" "g"
See the R demo.
So, the search items are properly escaped to be used in regex, they are sorted by length in descending order, the regex pattern based on alternation is built dynamically, then all matching and non-matching strings are found and then they are joined into a single character vector and empty items are discarded in the end.

Answer 4

One option to get your matches might be to us an alternation:
[a-z.]+|\[+|[+-]
[a-z.]+ Match 1+ times a-z or dot
| Or
\[+ match 1+ times a [
|` or
[+-] Match + or -
Regex demo | R demo
For example, to get the matches:
library(stringr)
x <- "abc[[+de.f[-[[g"
str_extract_all(x, "[a-z.]+|\\[+|[+-]")