Reading within parentheses in MATLAB
6 views (last 30 days)
Show older comments
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.
0 Comments
Answers (3)
Stephen23
on 4 Apr 2017
Edited: Stephen23
on 4 Apr 2017
>> 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
Jan
on 4 Apr 2017
Edited: Jan
on 4 Apr 2017
[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)
4 Comments
Stephen23
on 5 Apr 2017
"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
on 5 Apr 2017
@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.
Joseph Cheng
on 4 Apr 2017
Edited: Joseph Cheng
on 4 Apr 2017
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.
2 Comments
Jan
on 4 Apr 2017
@Joseph: I get the error:
??? Index exceeds matrix dimensions.
Error in ==> @(x)str2double(x(find(x=='(')+1:find(x==')')+1))
Joseph Cheng
on 4 Apr 2017
oopse. that should be -1, clipboard didn't update i guess when i pasted in my script.
See Also
Categories
Find more on Environment and Settings in Help Center and File Exchange
Community Treasure Hunt
Find the treasures in MATLAB Central and discover how the community can help you!
Start Hunting!