The expression generated dynamically needs to be a complete expression. What this means is that if you take the pattern returned by the dynamic operator, it should be able to match as a standalone expression.

The dynamic portion of your pattern produces the expression “4″ which will match the number “4″, as opposed to being used as a quantifier for the greater expression which contains it. The way you handle this is to generate more of your expression as part of the dynamic component:

>> ptrn = ‘^(\d)((??(\\s+[A-D]){$1}))’;
>> [m,t]=regexpi(tst,ptrn,’match’,'tokens’,'once’)

m =

4 A B C D

t =

’4′ ‘ A B C D’

A few things to note here:

1) Changing the dynamic component to (??{$1}) is not enough, as it is still not a complete expression, just the quantifier.

2) You have to escape the \s in the expression, as the entire subexpression is parsed like a replace string for regexprep.

3) To capture the second portion, I needed to add another set of parenthesis, as dynamic expressions can not create new capturing groups.

I hope that helps,

-=>J

Something’s not working for me.

Why does the following use of a dynamic regular expression not return the same result as its static equivalent? Am I missing something about when dynamic expressions can be used in R2011a?

>> tst=’4 A B C D 3′;
>> ptrn=’^(\d)(\s+[A-D]){4}’;
>> [m,t]=regexpi(tst,ptrn,’match’,'tokens’,'once’)

m =

4 A B C D

t =

’4′ ‘ A B C D’

>> ptrn=’^(\d)(\s+[A-D]){(??$1)}’

ptrn =

^(\d)(\s+[A-D]){(??$1)}

>> [m,t]=regexpi(tst,ptrn,’match’,'tokens’,'once’)

m =

”

t =

{}

NOTE: The only thing that has changed is that I’ve replaced the number 4 with the dynamic regular expression (??$1) that should equate to exactly the same character ’4′, as per the tokens shown above. I also have the same problem when I use a dynamic function call, as in (?@return_same_character($1)). The token is definitely captured, but it seems like the string is not being properly updated before the final matching is attempted.

Thanks for you help on this; I’m stymied.

Regards,
Adrian

The same regex can be used in Perl: they just didn’t because it’s horrible :) Clear code is preferable unless you’re intentionally obfuscating.

use List::Util qw(shuffle); #List::Util is core
while (<>) {
  s{(?<=\w)(\w{2,})(?=\w)}{join '', shuffle split //, $1}e;
  print $_, "\n";
}

Code evaluation like this has always been possible in Perl 5 as far as I can tell.

We also have named capture groups, which are stored in the special hash %+ since changing the way regexes return would introduce inconsistency:

(dump function provided by Data::Dump)

use 5.010;
my @date = '11/26/1977' =~ m{(\d+)/(\d+)/(\d+)};
dump \@date;

# [11, 26, 1977]

'11/26/1977' =~ m{(?\d+)/(?\d+)/(?\d+)};
my %date = %+;

dump \%date;

# { day => 26, month => 11, year => 1977 }

This is a feature of 5.10. Although many places are still running 5.8.8 it’s hardly Perl’s fault that people can’t keep up :) 5.10 is itself end-of-life; 5.14 is current and 5.12 is considered old.

Case preservation is a thing we don’t do. I suspect if you ask one of the core team why they will give you one of two answers:

1. We don’t know of anyone who has ever wanted it
2. We can’t make it work in a consistent way.

Kirk out

Happy holidays,
Brad

I have the same troubles with regexp as you describe and would love to see a GUI that could help me out! Please make this into an enhancement request by using the support link on the right side of my blog. Thanks!

–Loren

Consequently, If I’m doing anything even slightly non-trivial, it can be very time-consuming to work out the proper match expression by trial-and-error at the MATLAB command-line.

In desperation I Googled for a Reg. Expr. utility & found a free .NET-based offering called Expresso. This is a multi-pane app (similar in look to MATLAB) that allows one to see (in a tree view) how match expressions parse out. It’s really lowered the stress-level for me & speeds things up dramatically when I have to use regexp() in MATLAB.

IMHO, the Mathworks should consider offering some kind of analyzer like Expresso within the MATLAB environment. Otherwise, in my experience, reg. expr’s can be a real bottleneck for rapid code development.

Any comments appreciated,
Respectfully,
Brad

str2double(c{7,31}{1})

long live braces. Thanks for the platform.

How do I use str2double? For a 1X1 cellarray
str2double(c{1}{1});
seems to work as an argument to str2double. I cannot figure out what would work for later elements of the cellarray.

The documentation covers what MATLAB supports.

–Loren