regular expressions resources and regular expression problem

2 visualizzazioni (ultimi 30 giorni)
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

Risposta accettata

Andrei Bobrov
Andrei Bobrov il 30 Set 2012
Modificato: Andrei Bobrov il 30 Set 2012
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')
  3 Commenti
Daniel Shub
Daniel Shub il 30 Set 2012
Your regexp foo is so much better than mine. I always have to make things up.

Accedi per commentare.

Più risposte (3)

Ned Gulley
Ned Gulley il 8 Mag 2013
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 il 30 Set 2012
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 il 30 Set 2012
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.
  2 Commenti
Walter Roberson
Walter Roberson il 30 Set 2012
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.)
Patrick Mboma
Patrick Mboma il 30 Set 2012
Thanks Walter. It is something I will look into.

Accedi per commentare.

Categorie

Scopri di più su Characters and Strings in Help Center e File Exchange

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by