Identifying substrings based on complex rules

Question

Assume I have text strings that look something like this:

A-B-C-I1-I2-D-E-F-I1-I3-D-D-D-D-I1-I1-I2-I1-I1-I3-I3

Here I want to identify sequ

Answer 1

Try the following expression: (.*?)(?:I[0-9]-)*I3(?:-I[0-9])*. See the match groups: https://regex101.com/r/yA6aV9/1

Answer 2

Use strsplit

> x <- "A-B-C-I1-I2-D-E-F-I1-I3-D-D-D-D-I1-I1-I2-I1-I1-I3-I3"
> strsplit(x, "(?:-?I\\d+)*-?\\bI3-?(?:I\\d+-?)*")
[[1]]
[1] "A-B-C-I1-I2-D-E-F" "D-D-D-D"

> strsplit("A-B-I3-C-I3", "(?:-?I\\d+)*-?\\bI3\\b-?(?:I\\d+-?)*")
[[1]]
[1] "A-B" "C" 

or

> strsplit("A-B-I3-C-I3", "(?:-?I\\d+)*-?\\bI3\\b-?(?:I3-?)*")
[[1]]
[1] "A-B" "C"

Answer 3

You can identify the sequences which contains I3 with following regex :

(?:I\\d-?)*I3(?:-?I\\d)*

So you can split your text with this regex to get the desire result.

See demo https://regex101.com/r/bJ3iA3/4