how can I extract special contents of a text?

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ali 2016-4-11

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评论： ali 2016-4-11

given a text with several parenthesis in format of (a,b). how can I extract contents of these parenthesis( a and b)? I used textscan and regexp but unsuccessful.

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Walter Roberson 2016-4-11

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Are the parenthesis "nested", such as

(a,(b,c))

? Nested parenthesis are a nuisance to deal with.

ali 2016-4-11

@Walter No, it's not nested. Guillaume's answer worked. Thanks.

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Answer 1

Guillaume 2016-4-11

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regexp(yourstring, '(?<=\()[^)]+', 'match')

should do it. It matches any sequence of anything but closing brackets preceded by an opening bracket. Note that the opening bracket has to be escaped as it's a special character in regexes.

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Guillaume 2016-4-11

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(?<= starts a look-behind. It tells the regular expression engine to look for something before the match
\(| is the something in the look-behind. It is basically an opening bracket. Because opening brackets have special meaning in regular expression, it has to be escaped with |\.
) closes the look-behind, so the whole-look behind expression is (?<=\(), which tells the regular expression that a match must be immediately preceded by an opening bracket.
[^)]+ means match one or more and as many (the +) of anything that is not (the ^) a closing bracket (the )).

Therefore, the regular expression matches anything preceded by an opening bracket up to a closing bracket (or the end of the string).

If the (or the end of the string) bothers you, you could make sure that the anything is actually followed by a closing bracket by adding a look-ahead expression:

regexp(yourstring, '(?<=\()[^)]+(?=\))', 'match')

As per Walter's comment, this won't work when you have nested parenthesis. But regular expression are not really suited for arbitrary nesting. You would have to write a proper parser in that case.

ali 2016-4-11