First up is the lookbehind which works just fine: strsplit(x, '(?<=)', perl = TRUE) Since I still needed the delimiter as it contained useful information, I used the lookaround regular expressions. I had a string like c('3D/MON&SUN') and wanted to separate it by / and &. In the cheat sheet you can also find the part that gave me the trouble: lookarounds lookaroundsД«ack to my problem. Since regular expressions can get quite complicated really fast, I will stop here and refer you to a cheat sheet for more infos. If you instead want all numbers followed by a upper case letter you should use regular expressions: x <- c('3D', '4D', '3a') If you are looking for a specific pattern in a string вЂ“ let's say '3D' вЂ“ you can just use those characters: x <- c('3D', '4D', '3a') There is a also fixed = TRUE which can be considered to use a literal regular expression. Two types of regular expressions are used in R, extended regular expressions (the default) and Perl-like regular expressions used by perl = TRUE. With regular expressions you can describe patterns in a string and then use them in functions like grep, gsub or strsplit.ДЄs the R (3.4.1) help file for regex states:ДЄ regular expression is a pattern that describes a set of strings. If you do not know what regular expressions are, I will give you a short introduction. I wanted to split the string but also keep the delimiter. However, recently I came across a problem I could not get my head around. Even if you have some complex rule for the split, most of the time you can solve this with a regular expression. It is quite useful if you want to separate a string by a specific character. One of the functions I use the most is strsplit.

Perl split string