How to further extract a match values from a regexp match

Hello,

Had a quick question regarding regexp.

Let's say you have some string and you want to extract certain values from it

string='hello_1_goodbye_0.23_hi_1.55_exit_1000'
regexp(string,'hello_\d+\.*\d*','match')
>>>
1x1 cell array
('hello_1')

From here I'd like to just extract the number. I'm not super familiar with matlab, but in python for example, in a regex search you can use parenthesis than extract the specific group of your match

pattern='hello_(\d+\.*\d*)'
regex_search.group(1)='1'

So the pattern is the same and you are still matching hello_1, but from there you are able to extract only the numerical value

Answer 1

[Vilém Frynta]

If you use 'tokens' instead of match.

string = 'hello_2_goodbye_0.23_hi_1.55_exit_1000';
pattern = 'hello_(\d+\.*\d*)';

match = regexp(string, pattern, 'tokens');
num = match{1}   % can be converted to number from a string

ans = 1×1 cell array
    {'2'}

num = '2'

[Sam Mahdi]

Ah thank you. I was getting an error because I was just trying to print out

regexp(string, pattern, 'tokens','match');

And kept getting errors regarding not enough outputs specified for tokens option. Thought maybe I was using it wrong, just had to remove the match option. Thank you!

[Stephen23]

You might also want to use the ONCE option, to reduce the cell array nesting by one level:

S = 'hello_2_goodbye_0.23_hi_1.55_exit_1000';
P = 'hello_(\d+\.*\d*)';
C = regexp(S, P, 'tokens','once')

C = 1×1 cell array
    {'2'}