negative with positive lookbehind regex issue

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Sebastian
Sebastian 2016-7-17
评论： Sebastian 2016-7-18
I'm trying to find the location of open parenthesis, '(', that are preceded by a number, but not when that number is an integer also preceded by the characters 'O' or 'S'.
Example:
str = '12()+F34()+O56()';
should return ind = [3,9], i.e. the open parenthesis following the 12 and 34, but not O56
I tried this:
ind = regexp(str,'(?<=((?<![OS])[0-9]+))[\(]');
but it gives me all of them (ind:[3,9,15]). It does however exclude the cases when there is just a single number after 'O' or 'S' (e.g. str = '12()+F34()+O5()'; -> ind:[3,9])
Does anyone know the proper regular expression for this?
Matlab version: 7.13.0.564 (R2011b)
  1 个评论
Stephen23
Stephen23 2016-7-18
编辑：Stephen23 2016-7-18
@Sebastian: You might like to try using my FEX submission makeregexp:
http://www.mathworks.com/matlabcentral/fileexchange/48930-interactive-regular-expression-maker
which lets you interactively develop regular expressions and see regexp's outputs change as you type.

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采纳的回答

Stephen23
Stephen23 2016-7-18
编辑：Stephen23 2016-7-18
Try this regular expression: |(?<=\d+)(?<![OS]\d+)\(|
It relies on the fact that lookaround operations do not consume any characters: the first lookaround matches some digits, the second then checks that any digits are not preceded by the letters O or S. Here it is tested:
>> str = '12()+F34()+O56()';
>> regexp(str,'(?<=\d+)(?<![OS]\d+)\(')
ans =
3 9
To help develop this regular expression I used my FEX submission makeregexp:
http://www.mathworks.com/matlabcentral/fileexchange/48930-interactive-regular-expression-maker
which lets you interactively develop regular expressions and see regexp's outputs change as you type.
  1 个评论
Sebastian
Sebastian 2016-7-18
"lookaround operations do not consume any characters"
Of course, how did I forget. That explains everything. Thanks for the nice regex too.

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更多回答（1 个）

Azzi Abdelmalek
Azzi Abdelmalek 2016-7-17
str = '12()+F34()+O56()';
ii1=regexp(str,'(?<=[OS]\d+)(\()' )
ii2=regexp(str,'(?<=\d+)(\()' )
out=setdiff(ii2,ii1)
  1 个评论
Stephen23
Stephen23 2016-7-18
编辑：Stephen23 2016-7-18
Sebastian's "Answer" moved here:
Thanks Azzi, I will consider that solution. Do you know what is wrong with my initial expression?
Right now I'm resorting to
ind = [regexp(strFunc,'(?<=[^OS0-9][0-9]+)[\(]'),regexp(strFunc,'^[0-9]+[\(]','end')]
which seems to get the job done, but is not exactly the prettiest.

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