I'm trying to split a string containing two entries and each entry has a specific format:

• Category (e.g. active site/region) which is followed by a :
• Term (e.g. His, Glu/nucleotide-binding motif A) which is followed by a ,

Here's the string that I want to split:

string <- "active site: His, Glu,region: nucleotide-binding motif A,"

This is what I have tried so far. Except for the two empty substrings, it produces the desired output.

unlist(str_extract_all(string, ".*?(?=,(?:\\w |$))"))

[1] "active site: His, Glu"              ""                                   "region: nucleotide-binding motif A"
[4] "" 

How do I get rid of the empty substrings?

CodePudding user response：

You get the empty strings because .*? can also match an empty string where this assertion (?=,(?:\\w |$)) is true

You can exclude matching a colon or comma using a negated character class before matching :

[^:,\n] :.*?(?=,(?:\w|$))

Explanation

• [^:,\n] Match 1 chars other than : , or a newline
• : Match the colon
• .*? Match any char as least as possbiel
• (?= Positive lookahead, assert that what is directly to the right from the current position:
  • , Match literally
  • (?:\w|$) Match either a single word char, or assert the end of the string
• ) Close the lookahead

Regex demo | R demo

string <- "active site: His, Glu,region: nucleotide-binding motif A,"
unlist(str_extract_all(string, "[^:,\\n] :.*?(?=,(?:\\w|$))"))

Output

[1] "active site: His, Glu"              "region: nucleotide-binding motif A"

CodePudding user response：

Much longer and not as elegant as @The fourth bird 1, but it works:

library(stringr)

string2 <- strsplit(string, "([^,] ,[^,] ),", perl = TRUE)[[1]][2]
string1 <- str_replace(string, string2, "")
string <- str_replace_all(c(string1, string2), '\\,$', '')

> string
[1] "active site: His, Glu"             
[2] "region: nucleotide-binding motif A"