replace comma with dot in large array

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JB
JB el 18 de Ag. de 2017
Comentada: Image Analyst el 18 de Ag. de 2017
Please help, I'm new to matlab coding. I have a array like this
data={'250,1000' '-6,52796' '322,683' '1,50367'
'250,0500' '-6,54959' '322,695' '1,50379'
'250,0000' '-6,63267' '322,711' '1,50395'}
except that it is very large (4500 lines). I want to replace all the commas with dots and convert to a data matrix. So far I have this:
data = strrep(data, ',', '.');%replace ´,´ with ´.´
data=cellfun(@str2num,data);
which can do the trick but it is very slow. Any suggestions to speed up the process?

Respuesta aceptada

Guillaume
Guillaume el 18 de Ag. de 2017
Well, the slow bit is probably your cellfun(@str2num). Replacing that by:
data = str2double(data);
would probably be faster. The strrep step is already as fast as it can be in matlab.
If you want faster, you need to modify your import process but if I recall correctly matlab is not very good as coping with ',' decimal separator.
  1 comentario
JB
JB el 18 de Ag. de 2017
the code: dataS1 = str2double(strrep(dataS1, ',', '.'));
did the job in 0.21 sec. Thanks a lot. My old code was 3.6 sec...

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Image Analyst
Image Analyst el 18 de Ag. de 2017
4500 is not very big. I ran this code
% Create sample data
n = 4500
data = cell(1, n);
for k = 1 : n
data{k} = '123,456';
end
% Now do the replacement.
tic;
data = strrep(data, ',', '.'); % Replace ´,´ with ´.´
toc;
% celldisp(data);
fprintf('Done!\n');
and got this:
Elapsed time is 0.002293 seconds.
Two milliseconds seems fast to me. Exactly how fast do you need it?
  2 comentarios
JB
JB el 18 de Ag. de 2017
Editada: JB el 18 de Ag. de 2017
Hi Image analyst. It sure is faster than my code, but it does not convert to a data matrix. I might have made a mistake...
Image Analyst
Image Analyst el 18 de Ag. de 2017
"data matrix" is so ambiguous that we don't know what it is. ANY kind of matrix in MATLAB could be considered a data matrix, from a character matrix to a cell array to a table to a regular double matrix. Your "data" is a cell array and so is, in fact, already a data matrix. If you want a vector of doubles, you can do
d = str2double(data);
as Guillaume first showed. Did you ever figure out why yours took so long while my running of your code took only 2 ms?

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