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How do I split a string on highly structured/nested data?

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Contributed by Anonymous Monk on Jun 07, 2000 at 03:27 UTC
Q&A  > regular expressions


Description:

How do I split on complicated possiblities? For instance, "a,b,op2(c,d),op3(e,op4(f,g))" should be split into
a
b
op2(c,d)
op3(e,op4(f,g))
where c,d,e,f,g may be of the same form op(x,y).

In other words, I only want the split to occur at the highest level of commas and ignore the nested ones.

Answer: How do I split a string on highly structured/nested data?
contributed by lhoward

One approach is to use a parser like Parse::RecDescent. A real parser (as opposed to parsing a string with a regular expression alone) is much more powerful and can be more apropriate for parsing highly structured/nested data like your example.

use Parse::RecDescent; my $teststr="a,b,op2(c,d),op3(e,op4(f,g))"; my $grammar = q { content: /[^\)\(\,]+/ function: content '(' list ')' value: content item: function | value list: item ',' list | item startrule: list }; my $parser = new Parse::RecDescent ($grammar) or die "Bad grammar!\n"; defined $parser->startrule($teststr) or print "Bad text!\n";
For other approaches see the discussion on Balancing Parens.
Answer: How do I split a string on highly structured/nested data?
contributed by Anonymous Monk

This should work more reliably in case there are repeated strings:

$_ = "a,b,op2(c,d),(e),(f),(f,g),op3(e,op4(f,g))\n"; print; ($re=$_)=~s/((\()|(\))|.)/$2\Q$1\E$3/gs; @$ = (eval{/$re/}); die $@ if $@=~/unmatched/; $re = join'|',map{quotemeta}@$; print join"\n",/((?:$re|[^,])+)/g;
Answer: How do I split a string on highly structured/nested data?
contributed by merlyn

lhoward's grammar seems unnecessarily complicated. Let's simplify it a bit, as well as grabbing what is needed for the answer (the split items):

use Parse::RecDescent; my $teststr="a,b,op2(c,d),op3(e,op4(f,g))"; my $grammar = q { startrule: list list: <leftop: item ',' item> item: word '(' list ')' <commit> { "$item[1](".join(",",@{$item[3]})." +)" } | word word: /\w+/ }; my $parser = new Parse::RecDescent ($grammar) or die "Bad grammar!\n"; + defined (my $result = $parser->startrule($teststr)) or print "Bad text +!\n"; print map "<<< $_ >>>\n", @$result;
Yes, there it is. $result is an array ref of the split-apart items.

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