Extracting string from clojure collections using regex

Question

can you suggest me the shortest and easiest way for extracting substring from string sequence? I'm getting this collection from using enlive framework, which takes content from certain web page, and here is what I am getting as result:

("background-image:url('http://s3.mangareader.net/cover/gantz/gantz-r0.jpg')"
 "background-image:url('http://s3.mangareader.net/cover/deadman-wonderland/deadman-wonderland-r0.jpg')"
 "background-image:url('http://s3.mangareader.net/cover/12-prince/12-prince-r1.jpg')" )

What I would like is to get some help in extracting the URL from the each string in the sequence.i tried something with partition function, but with no success. Can anyone propose a regex, or any other approach for this problem?

Thanks

Arthur Ulfeldt · Accepted Answer · 2012-05-08 21:40:00Z

5

re-seq to the resque!

(map #(re-seq #"http.*jpg" %) d)
(("http://s3.mangareader.net/cover/gantz/gantz-r0.jpg")  
("http://s3.mangareader.net/cover/deadman-wonderland/deadman-wonderland-r0.jpg") 
("http://s3.mangareader.net/cover/12-prince/12-prince-r1.jpg"))
user>

re-find is even better:

user> (map #(re-find #"http.*jpg" %) d)
("http://s3.mangareader.net/cover/gantz/gantz-r0.jpg" 
 "http://s3.mangareader.net/cover/deadman-wonderland/deadman-wonderland-r0.jpg" 
 "http://s3.mangareader.net/cover/12-prince/12-prince-r1.jpg")

because it doesn't add an extra layer of seq.

edited May 8, 2012 at 21:40

answered May 8, 2012 at 19:54

Arthur Ulfeldt

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4 Comments

Мitke Over a year ago

Hi, great solution, thanks a ton !!!! By the way , can you recommend me a tutorial for regex in clojure, in order to avoid asking for help each time I have to tangle with them?

Arthur Ulfeldt Over a year ago

I would love to find that as well, anyone?

Retief Over a year ago

The best thing I can think of is calling (find-doc #"^re-") and reading the results. I don't know of anything better.

mikera Over a year ago

For regex syntax itself, worth noting that it is the same as Java, so any of the many Java tutorials are relevant e.g. tutorials.jenkov.com/java-regex/syntax.html

Jeremy · Accepted Answer · 2012-05-08 20:00:02Z

2

Would something simple like this work for you?

(defn extract-url [s]
  (subs s (inc (.indexOf s "'")) (.lastIndexOf s "'")))

This function will return a string containing all the characters between the first and last single quotes.

Assuming your sequence of strings is named ss, then:

(map extract-url ss)
;=> ("http://s3.mangareader.net/cover/gantz/gantz-r0.jpg"
;    "http://s3.mangareader.net/cover/deadman-wonderland/deadman-wonderland-r0.jpg"
;    "http://s3.mangareader.net/cover/12-prince/12-prince-r1.jpg")

This is definitely not a generic solution, but it fits the input you have provided.

edited May 8, 2012 at 20:00

answered May 8, 2012 at 19:51

Jeremy

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1 Comment

Мitke Over a year ago

Yup, it works like a charm. I thought this can be done more elegantly by regex, but this is way more comprehensive to OO guy like me. Thanks

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