Regular expression. Are nesting of group operators supported?

Question

per isakson 2018-12-17

2
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/436217-regular-expression-are-nesting-of-group-operators-supported

编辑： per isakson 2019-10-14

Regarding Grouping Operators the function, regexp, doesn't behave the way I expected.

>> cac = regexp( 'ABC', '((A)(B(C)))', 'tokens' );
>> cac{1}(:)
ans =
  1×1 cell array
    {'ABC'}

regexp returns one token without any protests regarding my parentheses. I expected four: 'ABC', 'A', 'BC' and 'C'. The reason I expected that is because most other flavors of regular expressions would have returned four tokens. Java: Capturing Groups would

In the expression ((A)(B(C))), for example, there are four such groups:

((A)(B(C)))
(A)
(B(C))
(C)

Another couple of examples

>> cac = regexp( 'ABC', '(A)(B(C))', 'tokens' );
>> cac{1}(:)
ans =
  2×1 cell array
    {'A' }
    {'BC'}
    
>> cac = regexprep( 'ABC', '((A)(B(C)))', ' --- $1 ---' )
cac =
    ' --- ABC ---'
>> cac = regexprep( 'ABC', '((A)(B(C)))', ' --- $2 ---' )
cac =
    ' --- $2 ---'    

The documentation on Grouping Operators is terse and there are only few examples. I've found nothing on "groups inside groups".

Question:

Are nesting of group operators supported or am I a victim of wishful thinking?

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Answer 1

Sean de Wolski 2018-12-17

2
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https://ww2.mathworks.cn/matlabcentral/answers/436217-regular-expression-are-nesting-of-group-operators-supported#answer_352857

编辑：Sean de Wolski 2018-12-17

在 MATLAB Online 中打开

The Note below "Named Token Operator" indicates that the outermost will be captured, hence ABC and one token.

Note

If an expression has nested parentheses, MATLAB® captures tokens that correspond to the outermost set of parentheses. For example, given the search pattern '(and(y|rew))', MATLAB creates a token for 'andrew' but not for 'y' or 'rew'.

With string arrays, I'd recommend just creating an array of acceptable tokens:

cac = regexp("ABC", ["(ABC)","(A)", "(BC)", "(C)"], 'tokens' );
cac{:}
ans =
  1×1 cell array
    {["ABC"]}
ans =
  1×1 cell array
    {["A"]}
ans =
  1×1 cell array
    {["BC"]}
ans =
  1×1 cell array
    {["C"]}