Extract all substrings in string

Question

I want to extract all substrings that begin with M and are terminated by a *

The string below as an example;

vec<-c("SHVANSGYMGMTPRLGLESLLE*A*MIRVASQ")

Would ideally return;

MGMTPRLGLESLLE
MTPRLGLESLLE

I have tried the code below;

regmatches(vec, gregexpr('(?<=M).*?(?=\\*)', vec, perl=T))[[1]]

but this drops the first M and only returns the first string rather than all substrings within.

"GMTPRLGLESLLE"

Answer 1

You can use

(?=(M[^*]*)\*)

See the regex demo. Details:

• (?= - start of a positive lookahead that matches a location that is immediately followed with:
• (M[^*]*) - Group 1: M, zero or more chars other than a * char
• \* - a * char
• ) - end of the lookahead.

See the R demo:

library(stringr)
vec <- c("SHVANSGYMGMTPRLGLESLLE*A*MIRVASQ")
matches <- stringr::str_match_all(vec, "(?=(M[^*]*)\\*)")
unlist(lapply(matches, function(z) z[,2]))
## => [1] "MGMTPRLGLESLLE" "MTPRLGLESLLE" 

If you prefer a base R solution:

vec <- c("SHVANSGYMGMTPRLGLESLLE*A*MIRVASQ")
matches <- regmatches(vec, gregexec("(?=(M[^*]*)\\*)", vec, perl=TRUE))
unlist(lapply(matches, tail, -1))
## => [1] "MGMTPRLGLESLLE" "MTPRLGLESLLE"