How to capture an optional expression using regular expressions?

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Patrick Mboma
Patrick Mboma 2015-9-23
评论： Walter Roberson 2015-9-25
Dear all,
I would like to use regular expressions to capture and transform expressions of the form
name
or
name(string,digits)
where name belongs to a list of NAMES and digits is an integer: 1, 2, 3,...
That is, "name" is optionally followed by
  1. an opening parenthesis: (
  2. a string
  3. some numbers : 1, 2, 3,...
  4. a closing parenthesis: )
For that purpose I wrote the following regular expression that does not work
expr='(\w+)((\w+),(\d+))?'
replace='${convertMe($1,$3,$4)}';
result=regexprep(cellarray,expr,replace)
I have written a convertMe function taking 3 inputs but only the first input gets in. The other inputs the function receives are $3 and $4 instead of the second string and the digits.
Any suggestions?

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回答（2 个）

Walter Roberson
Walter Roberson 2015-9-23
For the longer case, expr='(\w+)(?:\(\w+),\(d+)\))' replace='${convertMe($1,$2,$3)}'
For the case with no argument supplied, it is not clear what you would like passed to convertMe or if you want convertMe to be called at all.
  2 个评论
Patrick Mboma
Patrick Mboma 2015-9-23
Hi Walter, Thanks for the answer. It seems to me that what you suggest has some problems. I tried to correct your suggestion as follows
expr='(\w+)(?:\((\w+),(\d+)\))'
But it still doesn't work. I do capture the first \w+ but not the second and not the \d+ . The second and third arguments received by convertMe are $2 and $3.
In the short case, I would like to capture only the first \w+ only. I would be fine if in that case convertMe receives $2 and $3 as the second and third input arguments respectively.

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Cedric
Cedric 2015-9-24
Another option is to parse all entries first, and then to rebuild relevant expressions:
entries = {'name1(John, 48)', 'name2', 'name3(Doo)'} ;
tokens = regexp( entries, '([\w\d_-]+)\(?(\w+)?,?\s*(\d+)?', 'tokens', 'once' ) ;
parsed = vertcat( tokens{:} ) ;
With that you get
>> parsed
parsed =
'name1' 'John' '48'
'name2' '' ''
'name3' 'Doo' ''
which is easy to post process for building whatever you need.

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