regular expressions resources and regular expression problem

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Patrick Mboma
Patrick Mboma 2012-9-30
Hi all, I don't know anything about regular expressions and I have two questions:
  1. What is the most effective way to learn regular expressions and where to find the best possible tutorials, examples, exercises etc.
  2. I have the following problem. I would like to extract (1) a list variables and (2) a list of matlab functions from a string. The variables have a precise definition: (i) they can start with 'a' 'd' or 'ee'; (2) then an underscore '_'; (3) then an integer 'n'. For example, the variables could be 'a_1', 'd_100', 'ee_3289' and the expression to parse could look like: 'cos(exp(a_2/4*d_1^3-ee_4)+d_85)'. In this example, the list of variables is 'a_2', 'd_1', 'ee_4', 'd_85' and the list of matlab functions is 'cos', 'exp'. My question here is what is the (best) regular expression to extract that information?
Thanks, Pat

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采纳的回答

Andrei Bobrov
Andrei Bobrov 2012-9-30
编辑：Andrei Bobrov 2012-9-30
1. Read here about the Regular Expressions
2.
str = 'cos(exp(a_2/4*d_1^3-ee_4)+d_85)';
fun = regexp(str,'\w*(?=\()','match')
var = regexp(str,'(a|d|ee)_\d*','match')
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Daniel Shub
Daniel Shub 2012-9-30
Your regexp foo is so much better than mine. I always have to make things up.

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更多回答（3 个）

Ned Gulley
Ned Gulley 2013-5-8
Another way to get good at regular expressions is to practice on Cody with all the problems that have been tagged "regexp".
Daniel Shub
Daniel Shub 2012-9-30
Assuming a string x,
[a, b] = regexp(x, '(a|d|(ee))(_)([0-9]*)', 'start', 'end')
will find the start and end indices of your "variables." This will allow for a variable a_0 which may or may not be desired. Without a rule for defining functions that handles the numerous edge cases, creating the regexp is difficult. Andrei's answer seems reasonable to me.
Patrick Mboma
Patrick Mboma 2012-9-30
Thank you both. That is one big problem solved. The biggest remains though: how do I become as good as you guys are with regular expressions?
Thanks a lot, Pat.
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Walter Roberson
Walter Roberson 2012-9-30
I think there is an O'Reilly book on regular expressions.
The regular expressions used in MATLAB are a mish-mash between capabilities in other languages. They have similarities to Perl, so it might make sense to study the resources for regular expressions in Perl (and there is probably a book or three for that topic alone.)

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