problem in writing Regular Expression

[Dawood Mohammed]

Hi,
I have a string from which i want to get strings seperated by space, which may also include string with double quotes.

for e.g: business political international "sports news" "local news" editorial

The result of parsing the above string with regular expression must be:
business
political
sports news
local news
editorial

please help me in solving this problem, this is pretty urgent.

Thanks and regards,
Dawood.

[Paul Sturrock]

What have you tried so far?

[Dawood Mohammed]

I have tried using lookahead, lookbehind regular expressions to solve this problem. but, couldnt work out how lookahead and lookbehind works

[Joanne Neal]

Originally posted by Dawood Mohammed:
please help me in solving this problem, this is pretty urgent.

Is it as urgent as your other problem ? I just need to know which to concentrate all my efforts on first.

Ease Up

[Ernest Friedman-Hill]

Neither of your two "regular expressions" problems are really very well-suited to regular expressions. They're really both simple state-machine type parsing problems, both simple enough to solve with an ad-hoc lexical analyzer, but each non-trivial enough to justify using something like ANTLR instead if you wanted to.

[Dawood Mohammed]

thanx for ur quick response. actually both the problems are very urgent for me as both of them are interrelated in my project.

[Dawood Mohammed]

Friedman,
Thanx for ur response. how do we use antlr or state machines in java program can u please give an example as I dont have any idea about antlr.

Thanx in advance

[Ernest Friedman-Hill]

Here is a tutorial on doing a very simple parsing problem with ANTLR.

[Kevin Davies]

This is an easy regex problem, don't waste your time trying to write your own lexer :

import java.util.ArrayList;
import java.util.List;
import java.util.regex.Matcher;
import java.util.regex.Pattern;
 
public class Parse {
    static Pattern pattern = Pattern.compile("\"([^\"]+)\"|(\\S+)");
 
    static List<String> parse(String string){
        Matcher matcher = pattern.matcher(string);
        ArrayList<String> list = new ArrayList<String>();
        while(matcher.find()){
            String value = matcher.group(1);
            if(value==null){
                value = matcher.group(2);
            }
            list.add(value);
        }
        return list;
    }
 
    public static void main(String[] args) {
        String input = "business political international \"sports news\" \"local news\" editorial";
        for(String token : parse(input)){
            System.out.println(token);
        }
    }
 
}
 

[Ernest Friedman-Hill]

Nice. I stand corrected.

[Dawood Mohammed]

Thanx a lot for ur solution Kevin Davies.

can u please give me the solution for my other question:

For the example below, can I write a regular expression to get key, value pairs.

example: ((abc def) (ghi jkl) (a ((b c) (d e))) (mno pqr) (a ((abc def))))

in the above example
abc is key & def is value
ghi is key & jkl is value
a is key & ((b c) (d e)) is value
and so on.


Thanks in advance

[Alan Moore]

"\\(([a-z]+) +((?:[a-z]+|\\((?:\\([^()]+\\) *)+\\)))\\)"

If you plug that into Kevin's code, you'll be able to retrive the keys via group(1) and the values via group(2). This works on the one line of sample data you provided, but YMMV. For instance, if you decide you need another level of parenthesis nesting, the regex will become about twice as ugly. I really think you're better off using a dedicated parser for this one.

[Layne Lund]

Regular expressions are not well suited for parsing nested parentheses. You will need a slightly more complicated parser that can count how many "levels" there are in the nesting. If you want to investigate this further on your own, you should google for "context free language", "context free grammar", or "push down automata" as these are the theoretical foundations for doing such parsing.

HTH

Layne