Reading within parentheses in MATLAB

I have a 100 x 1 cell array where each element consists of a number followed by a space followed by a number in parentheses. For example: 401 (106), 234 (113), 345 (120)...

I would like to create a new 100 x 1 cell array where each element consists of solely the number within the parentheses. That is: 106, 113, 120...

If there a way to do this in MATLAB? I was thinking about scanning each element and reading only the data after "(" and before ")", but I don't know how to go about doing it.

Answer 1

[Stephen23]

This is very easy with regexp:

>> C = {'401 (106)', '234 (113)', '345 (120)'};
>> D = regexp(C,'(\d+)\s+\((\d+)\)','tokens','once');
>> str2double(cell2mat(D))
ans =
        401        234        345
        106        113        120

[Guillaume]

Or you could use this slightly less strict regex:

str2double(regexp(C, '(?<=\()[^)]*', 'match', 'once'))

matches everything after (| up to |).

Answer 2

[Jan]

[EDITED] The former version replied both values, but the OP NP4432 asked for the value in parenthesis only.

C = {'401 (106)', '234 (113)', '345 (120)'};

D = sscanf(sprintf('%s ', C{:}), '%*g (%g)', [1, numel(C)]).';
R = num2cell(D, 2);

As usual a run-time comparison:

C = cell(1, 100);  % Test data
for k = 1:numel(C), C{k} = '401 (106)'; end

tic
for k = 1:100
  D  = sscanf(sprintf('%s ', C{:}), '%*g (%g)', [1, numel(C)]).';
  R1 = num2cell(D, 2);
end
toc

tic
for k = 1:100
  % D  = regexp(C,'(\d+)\s+\((\d+)\)','tokens','once');
  % R2 = str2double(cell2mat(D));  % Does not run on my old 2009a
  % R2 = str2double(cat(1, D{:}));
  D  = str2double(regexp(C, '(?<=\()[^)]*', 'match', 'once'));
  R2 = num2cell(D, 1);
end
toc

tic
for k = 1:100
  R3 = cellfun(@(x) sscanf(x, '%*g (%g)'), C, ...
               'Uniformoutput', false);
end
toc

R2009a/64, Win7, 2 cores of a i5 in a VM:

 Elapsed time is 0.187068 seconds.  % SSCANF & SPRINTF
 Elapsed time is 1.337538 seconds.  % REGEXP
 Elapsed time is 1.207764 seconds.  % CELLFUN(SSCANF)

[Stephen23]

+1 nice use of sscanf. Even simpler:

>> C = {'401 (106)', '234 (113)', '345 (120)'};
>> sscanf([C{:}],'%d (%d)')
ans =
   401
   106
   234
   113
   345
   120

[Jan]

@Stephen: The OP wants the number inside the parenthesis only. I had overseen this at first.

If speed matters: FEX: CStr2String:

num2cell(sscanf(CStr2String(C), '%*d (%d)'), 2)

It seems like [C{:}] has problems with the pre-allocation.

[Stephen23]

"The OP wants the number inside the parenthesis only"

Sure, and this is trivial with indexing:

 >> C = {'401 (106)', '234 (113)', '345 (120)'};
 >> V = sscanf([C{:}],'%d (%d)');
 >> V(2:2:end)

[Jan]

@Stephen: I have the old R2009a only during the day. I assume REGEXP of modern Matlab versions is faster. Could you post the output of the speed comparison? Thanks.

Answer 3

[Joseph Cheng]

since you've got the right idea and cellfun() is troublesome and sometimes confusing, i've coded it for you here:

dumdata = {'401 (106)',' 234 (113)',' 345 (120)'};
cellfun(@(x) str2double(x(find(x=='(')+1:find(x==')')-1)),dumdata,'Uniformoutput',false)

cellfun applies the function for each cell of the supplied cell array. otherwise this can be done in a for loop with implementing the what is shown in the anonymous function.

[Jan]

@Joseph: I get the error:

??? Index exceeds matrix dimensions.
Error in ==> @(x)str2double(x(find(x=='(')+1:find(x==')')+1))

[Joseph Cheng]

oopse. that should be -1, clipboard didn't update i guess when i pasted in my script.