Regexp IF statement
in [Matlab]
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From: Nicholas Heung on 23 Jul 2010 10:02 Hi, Using perl, I'm able to detect if a regex matches by doing an if statement - is this possible in MatLab, or would I just need to check if the results are empty? Thanks
From: Walter Roberson on 23 Jul 2010 10:31 Nicholas Heung wrote: > Using perl, I'm able to detect if a regex matches by doing an if > statement - is this possible in MatLab, or would I just need to check if > the results are empty? It depends which options you gave to regex about what it should return. An "if" statement will succeed if all of the values are non-zero. For example, if [3 5 9]; disp('this will be displayed'); end if [3 0 9]; disp('this will not be displayed'); end if []; disp('this will not be displayed either'); end if {}; disp('sorry this is invalid'); end Thus if you set regex to return the vector of start indices, you could code as if regex(String,Pattern,'start') and that would succeed if something matches. On the other hand, it is much clearer programming to explicitly indicate that you are testing a vector instead of the usual scalar if all(regex(String,Pattern,'start')) and in this particular case that would be equivalent to if ~isempty(regex(String,Pattern,'start')) Thus although you do not _need_ to test with isempty(), it is much more readable if you do. Note though that in perl, the match operator has side effects, setting $1 and so on. Matlab's regexp does not have those side effects, so the typical perl writing style becomes less common in Matlab.
From: Nicholas on 23 Jul 2010 11:00 Thanks, that was very helpful. Walter Roberson <roberson(a)hushmail.com> wrote in message <9Jh2o.47010$Ls1.30212(a)newsfe11.iad>... > Nicholas Heung wrote: > > > Using perl, I'm able to detect if a regex matches by doing an if > > statement - is this possible in MatLab, or would I just need to check if > > the results are empty? > > It depends which options you gave to regex about what it should return. > > An "if" statement will succeed if all of the values are non-zero. For > example, > > if [3 5 9]; disp('this will be displayed'); end > if [3 0 9]; disp('this will not be displayed'); end > if []; disp('this will not be displayed either'); end > if {}; disp('sorry this is invalid'); end > > Thus if you set regex to return the vector of start indices, you could > code as > > if regex(String,Pattern,'start') > > and that would succeed if something matches. > > > On the other hand, it is much clearer programming to explicitly indicate > that you are testing a vector instead of the usual scalar > > if all(regex(String,Pattern,'start')) > > and in this particular case that would be equivalent to > > if ~isempty(regex(String,Pattern,'start')) > > Thus although you do not _need_ to test with isempty(), it is much more > readable if you do. > > > Note though that in perl, the match operator has side effects, setting > $1 and so on. Matlab's regexp does not have those side effects, so the > typical perl writing style becomes less common in Matlab.
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