In a string containing nested parantheses, how do I remove all the inner pairs using Perl?

Question

Suppose you have a string like this

.((((((.(((((((((((((((((((((...((((...)))).((((...))))))))))))))))))))))))))))))).

and I want to omit the part ...((((...)))).((((...))) and get only the outer level of parenthesis. How can I do this in Perl?

Usually the strings I encounter in my work are something like this

(((((.(((((((((((((((((((((...((((((.....))))))..........))))))))))))))))))))))))))

and in this case it is easy to implement using index function to specify the position of the last ( and the first ), but in the nested case I tried using stacks to implement but it didn't work.

This is the first nested loop to be omitted .((((((.(((((((((((((((((((((...((((...)))).((((...))))))))))))))))))))))))))))))). and this is the second .((((((.(((((((((((((((((((((...((((...)))).((((...))))))))))))))))))))))))))))))). according to this I must omit all the characters in between these parenthesis .((((((.(((((((((((((((((((((...((((...)))).((((...))))))))))))))))))))))))))))))).

Are there really dots at those places in the input, or are you using them to denote that there are many more brackets? — Sundar R, Jul 24 '13 at 07:06

Ed Heal · Answer 1 · 2013-07-24T13:00:08.883

2

Use substitution i.e. the following s/<regular expression>//

Remember the brackets and full stop needs to be escaped.

EDIT

Here is the regular expression in the substitution

$var =~s%\.\.\.\(\(\(\(\.\.\.\)\)\)\)\.\(\(\(\(\.\.\.\)\)\)%%;

edited Jul 24 '13 at 13:00

answered Jul 24 '13 at 03:09

Ed Heal

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may you explain your idea. I didn't get it – user1351343 Jul 24 '13 at 03:29
@user1351343 - Please read the link and learn about regular expressions. – Ed Heal Jul 24 '13 at 03:37
I read it but I still don't understand how to use – user1351343 Jul 24 '13 at 12:48
you are considering this particular case, but I'm looking for general solution – user1351343 Jul 24 '13 at 13:15
@user1351343 - Your question is unclear. Guess you need to figure out how to use regular expressions. Useful thing to learn – Ed Heal Jul 24 '13 at 16:39

score 1 · Answer 2 · edited May 23 '17 at 10:25

1

You can use the code from this answer by the ingenious SO user ikegami

Parsing string with nested parentheses using Parse::RecDescent

with a slight modification: Change this line

STRING : /\w+/

to this

STRING : /[\w\.]+/

and then call the $parser->parse() method with some of your data.

You can also flatten the $tree using this code:

print(Dumper(flatten($tree)));


sub flatten {
    map { ref eq 'ARRAY' ? flatten(@$_) : $_ } @_
}

But maybe you have code already to process the parse tree generated.

edited May 23 '17 at 10:25

Community

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answered Jul 24 '13 at 07:41

knb

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I did but I got a lot of errors – user1351343 Jul 24 '13 at 13:00
so maybe your strings are not properly nested, or you have extra chars in your strings that you need to include in the regex. Can't really help you with messy data, sorry about that. – knb Jul 24 '13 at 14:37

In a string containing nested parantheses, how do I remove all the inner pairs using Perl?

2 Answers2