Create substring from string based on pattern and also retain the pattern inside the substring

Question

Is it possible to create substring from string based on pattern that matching a word but also retain the matching part ?

a <- "contrainte que ilz ne contraint Que ris et jeux mais ne contrainte que jamais on ne contrainte que vous ne contraindre que de ne contraint que l' amour ne contraint que je ne contrainte que je ne contraint que je ne contrainte que l' homme arrive à ne contraint que nous ne contrainte que je ne contraintes que le créateur ne contrainte que l' opium même ne"

I would love to split the string when the pattern is present which is "cont".

strsplit(a, "cont", perl = T)

 [1] ""                                 "rainte que ilz ne "               "raint Que ris et jeux mais ne "   "rainte que jamais on ne "        
 [5] "rainte que vous ne "              "raindre que de ne "               "raint que l' amour ne "           "raint que je ne "                
 [9] "rainte que je ne "                "raint que je ne "                 "rainte que l' homme arrive à ne " "raint que nous ne "              
[13] "rainte que je ne "                "raintes que le créateur ne "      "rainte que l' opium même ne"

What I would love to do is exactly the same but retain the match part inside to substring.

Thank you!

PKumar · Accepted Answer · 2018-06-20T11:39:03.997

2

You can use stringr::str_split with lookaheads, for example:

stringr::str_split(a, "(?=cont)")[[1]]

Lookarounds are zero width assertions, which means they don't eat any alphabets, so here: Positive lookahead works as to match anything(?=anyword) matches a anything that is followed by a anyword,

Output:

stringr::str_split(a, "(?=cont)")[[1]]
 [1] ""                                    
 [2] "contrainte que ilz ne "              
 [3] "contraint Que ris et jeux mais ne "  
 [4] "contrainte que jamais on ne "        
 [5] "contrainte que vous ne "             
 [6] "contraindre que de ne "              
 [7] "contraint que l' amour ne "          
 [8] "contraint que je ne "                
 [9] "contrainte que je ne "               
[10] "contraint que je ne "                
[11] "contrainte que l' homme arrive à ne "
[12] "contraint que nous ne "              
[13] "contrainte que je ne "               
[14] "contraintes que le créateur ne "     
[15] "contrainte que l' opium même ne"

edited Jun 20 '18 at 11:39

answered Jun 20 '18 at 11:36

PKumar

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Upvoted. Bonus points if you can explain why `strsplit(a, "(?=cont.*)", perl = T)` does _not_ work. – Tim Biegeleisen Jun 20 '18 at 11:37
I'm curious about that one too! That was my approach, and as @TimBiegeleisen points out, it does not work. – Maurits Evers Jun 20 '18 at 11:40
@MauritsEvers It's stopping at the first `c`. Don't know why. – Tim Biegeleisen Jun 20 '18 at 11:41
@TimBiegeleisen Yep, I noticed that too. I was hoping you knew why. – Maurits Evers Jun 20 '18 at 11:44
@TimBiegeleisen, Apprently this looks the correct answer: https://stackoverflow.com/questions/15575221/why-does-strsplit-use-positive-lookahead-and-lookbehind-assertion-matches-differ – PKumar Jun 20 '18 at 12:00

Create substring from string based on pattern and also retain the pattern inside the substring

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