Regex for replacing commas only within brackets-CodePudding

I have an ingredient dataset and each row is a list of ingredients that's separated by comma, for example:

Oats (24%) (Rolled, Bran), Coconut (13%) (Coconut , Preservative (220, 223)), Brown Sugar, Milk Solids, Golden Syrup (10%), Seeds (9%) (Sesame , Sunflower), Margarine (Vegetable Oil, Water, Salt, Emulsifiers (471, Soy Lecithin), Antioxidant (307)), Glucose, Milk Choc Compound (5%) (Sugar, Vegetable Oil, Milk Solids, Cocoa Powder, Emulsifiers (Soy Lecithin, 492), Natural Flavour), Natural Flavour

I want to parse the file to replace only commas within brackets with a semicolon. There can be any number of brackets and any number of commas within the brackets. The result should look like this:

Oats (24%) (Rolled;Bran), Coconut (13%) (Coconut ; Preservative (220; 223)), Brown Sugar, Milk Solids, Golden Syrup (10%), Seeds (9%) (Sesame ;Sunflower), Margarine (Vegetable Oil; Water; Salt; Emulsifiers (471; Soy Lecithin); Antioxidant (307)), Glucose, Milk Choc Compound (5%) (Sugar; Vegetable Oil; Milk Solids; Cocoa Powder; Emulsifiers (Soy Lecithin; 492); Natural Flavour), Natural Flavour

Can I get some help on regex that will solve the problem? Thank you in advance.

CodePudding user response：

1) gsubfn This can be done without complex regular expressions using gsubfn. The regular expression consisting of a dot matches a single character. Then for each match fun is run with that character passed to it via the x argument. this$k within fun refers to a counter that starts at 0 and is incremented by 1 each time a ( is encountered and decremented by 1 each time a ) is encountered. If the counter is not zero and a comma is encountered a semicolon is returned to replace the comma; otherwise, the input character is returned.

library(gsubfn)

p <- proto(k = 0, fun = function(this, x) {
  if (x == "(") this$k <- k   1
  if (x == ")") this$k <- k - 1
  if (k && x == ",") ";" else x
})
gsubfn(".", p, s)

giving:

[1] "Oats (24%) (Rolled; Bran), Coconut (13%) (Coconut ; Preservative (220; 223)), Brown Sugar, Milk Solids, Golden Syrup (10%), Seeds (9%) (Sesame ; Sunflower), Margarine (Vegetable Oil; Water; Salt; Emulsifiers (471; Soy Lecithin); Antioxidant (307)), Glucose, Milk Choc Compound (5%) (Sugar; Vegetable Oil; Milk Solids; Cocoa Powder; Emulsifiers (Soy Lecithin; 492); Natural Flavour), Natural Flavour"

2) Base R A base R solution is to split the input into single characters giving character vector chars and then create a counter vector, k, the same length as chars which indicates the number of ( up to each character minus the number of ). Then replace those commas corresponding to a nonzero k with semicolon and transform chars back to a single string.

chars <- strsplit(s, "")[[1]]
k <- cumsum((chars == "(") - (chars == ")"))
chars[k & chars == ","] <- ";"
paste(chars, collapse = "")

Note

Input string s is the following.

s <- "Oats (24%) (Rolled, Bran), Coconut (13%) (Coconut , Preservative (220, 223)), Brown Sugar, Milk Solids, Golden Syrup (10%), Seeds (9%) (Sesame , Sunflower), Margarine (Vegetable Oil, Water, Salt, Emulsifiers (471, Soy Lecithin), Antioxidant (307)), Glucose, Milk Choc Compound (5%) (Sugar, Vegetable Oil, Milk Solids, Cocoa Powder, Emulsifiers (Soy Lecithin, 492), Natural Flavour), Natural Flavour"

CodePudding user response：

You can use ?R like.

i <- gregexpr("\\(([^()]|(?R))*\\)", s, perl=TRUE)
regmatches(s, i)[[1]] <- gsub(",", ";", regmatches(s, i)[[1]])

s
#[1] "Oats (24%) (Rolled; Bran), Coconut (13%) (Coconut ; Preservative (220; 223)), Brown Sugar, Milk Solids, Golden Syrup (10%), Seeds (9%) (Sesame ; Sunflower), Margarine (Vegetable Oil; Water; Salt; Emulsifiers (471; Soy Lecithin); Antioxidant (307)), Glucose, Milk Choc Compound (5%) (Sugar; Vegetable Oil; Milk Solids; Cocoa Powder; Emulsifiers (Soy Lecithin; 492); Natural Flavour), Natural Flavour"

Where a(?R)z is a recursion which match one or more letters a followed by exactly the same number of letters z.

Data

s <- "Oats (24%) (Rolled, Bran), Coconut (13%) (Coconut , Preservative (220, 223)), Brown Sugar, Milk Solids, Golden Syrup (10%), Seeds (9%) (Sesame , Sunflower), Margarine (Vegetable Oil, Water, Salt, Emulsifiers (471, Soy Lecithin), Antioxidant (307)), Glucose, Milk Choc Compound (5%) (Sugar, Vegetable Oil, Milk Solids, Cocoa Powder, Emulsifiers (Soy Lecithin, 492), Natural Flavour), Natural Flavour"