Skip to content

Hep with regex! - combination of ^, |, \\, _ and $

9 messages · David Winsemius, Duncan Murdoch, Berend Hasselman +2 more

Original
Dimitri Liakhovitski
# 
(x <- c("q10_1", "q10_2", "q10_11", "q12_1", "q12_2", "q13_1", "q13_11"))

# Which strings start with "q10" or "q12? - WORKS
x[grep("^q10|q12", x)]

# Which strings end with "1"? - WORKS
x[grep("1$", x)]

# Which strings end with "_1"? - WORKS
x[grep("\\_1$", x)]

# Which strings start with "q10" AND contain a "1"? - WORKS
x[grep("^q10.+1", x)]

# Which strings start with "q10" AND end with a "_1"? - DOES NOT WORK
x[grep("^q10.+\\_1$", x)]

# Which strings start with "q10" or "q12 AND end with "_1"? - WORKS INCORRECTLY
x[grep("^q10|q12.+\\_1$", x)]

Thank you!
Dimitri Liakhovitski
Duncan Murdoch
#
On 17/09/2015 5:11 PM, Dimitri Liakhovitski wrote:
Your verbal description doesn't match your regexp, and you didn't show
us your output, so how can we tell whether this is you not understanding
regular expressions, or an actual problem?

When I try this example, I get

character(0)

which is the correct outcome, given the input string.

Duncan Murdoch
Dimitri Liakhovitski
# 
Duncan,
Of course my verbal descriptions and my code don't match my regexp -
otherwise I wouldn't be asking the question, would I?
Please assume my verbal descriptions are correctly describing what I want.
Thank you!

On Thu, Sep 17, 2015 at 5:42 PM, Duncan Murdoch
<murdoch.duncan at gmail.com> wrote:

  
    

      
      
    

  


  


      

    

    

      
      

        


  

        

      Dimitri Liakhovitski
    

    

      
      #
    

  


  

      
For the last one, looks like this one works:
x[grep("^(q10|q12).*\\_1$", x)]

On Thu, Sep 17, 2015 at 5:46 PM, Dimitri Liakhovitski

        
<dimitri.liakhovitski at gmail.com> wrote:

            

      
      
      
    

        

      
      
    

            

      
      
      
    

        

  
    

      
      
    

  


  


      

    

    

      
      

        


  

        

      David Winsemius
    

    

      
      #
    

  


  

      
On Sep 17, 2015, at 2:11 PM, Dimitri Liakhovitski wrote:

        

            

      
      
      
    

        
You solved the last one with grouping around the OR-operator. The penultimate error needs only a very slight change to find a single instance in x:

x[grep("^q10.*_1$", x)]
[1] "q10_1"

Using "+" requires at leas one character between the two end, whereas you use the "*" operator to allow for the possibility of no intervening characters.

  
    

      
      
    

  


  


      

    

    

      
      

        


  

        

      Duncan Murdoch
    

    

      
      #
    

  


  

      
On 17/09/2015 5:46 PM, Dimitri Liakhovitski wrote:

            

      
      
      
    

        
Sorry, I interpreted "works" and "does not work" to be saying that R's
regexp matching was working or not.

I think you've got your answers from others now...

Duncan Murdoch

            

      
      
      
    

        

      
      
    

            

      
      
      
    

  
  


  


      

    

    

      
      

        


  

        

      Berend Hasselman
    

    

      
      #
    

  


  

          

      
      
      
    

        
For these last to this should ?work?

            

      
      
      
    

        
x[grep("^q10.*\\_1$", x)]

            

      
      
      
    

        
x[grep("^q10|q12.*\\_1$", x)]

It?s the .+ that?s the problem.

Berend

            

      
      
      
    

        

      
      
    

  
  


  


      

    

    

      
      

        


  

        

      Upton, Stephen (Steve) (CIV)
    

    

      
      #
    

  


  

      
And unless I'm mistaken, escaping the underscore is superfluous (I'd be curious to know if it's a function of locale).

x[grep("_", x)]

x[grep("^q10.*_1$", x)]

both work.

steve

Stephen C. Upton
SEED (Simulation Experiments & Efficient Designs) Center
Operations Research Department
Naval Postgraduate School
SEED Center web site: http://harvest.nps.edu

-----Original Message-----
From: R-help [mailto:r-help-bounces at r-project.org] On Behalf Of Berend Hasselman
Sent: Friday, September 18, 2015 1:30 AM
To: Dimitri Liakhovitski
Cc: r-help
Subject: Re: [R] Hep with regex! - combination of ^, |, \\, _ and $

            

      
      
      
    

        
For these last to this should ?work?

            

      
      
      
    

        
x[grep("^q10.*\\_1$", x)]

            

      
      
      
    

        
x[grep("^q10|q12.*\\_1$", x)]

It?s the .+ that?s the problem.

Berend

            

      
      
      
    

        

      
      
    

        
______________________________________________
R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.

  
  


  


      

    

    

      
      

        


  

        

      Dimitri Liakhovitski
    

    

      
      #
    

  


  

      
Thank you very much, guys!
As always - great learnings for me! Esp. + vs. *

On Fri, Sep 18, 2015 at 8:48 AM, Upton, Stephen (Steve) (CIV)

        
<scupton at nps.edu> wrote: