MATLAB: Is it possible to fill a structure in a parfor

parforstructures

Hi everyone,
I need to open a large number of CSV files. The files are indexed according to some variables "ENF" (that goes from i=1:I) and "Theta" (that goes from j=1:J). Each file contains a large number of rows and columns. The number of columns and rows differ across files.
I would like load the data into a structure like this:
dataStruct.(ENFi).(Thetaj) = FileName_i_j.csv
This is my code to load the data:
I = 50;              
J = 100;             
DirData = ('/Users/MyDir');
NameData1 = ('Name1');
NameData2 = ('Name2');
for i=1:I                      % I would like to parallel process this 
    fprintf('ENF: %4.0f \n', i)
    for j=1:J
        FileName = [DirData NameData1 num2str(i) NameData2 num2str(j)];
        Dat1 = ['ENF' num2str(i)];
        Dat2 = ['Theta' num2str(j)];
        dataStruct.(Dat1).(Dat2) = csvread([FileName '.csv']);
    end
end
This loop takes a while. I would like to parallel process the first "for". I thought it should be straightforward. However, I cannot figure out how to do it. Matlab complains about the data structure within the parfor.
Any suggestions or ideas?
Thanks. Javier

Best Answer

I haven't got the parallel processing toolbox but if matlab won't let you parallelise the dynamic field assignment the way I would solve it is by storing the content of these fields into a temporary cell array:
sfields = cell(1, I);
parfor i=1:I
   s = struct;
   %...

       sfields{i} = struct(Dat2, csvread(sprintf('%s.csv', FileName)));
   %...
   sfields{i} = s;
end
for i=1:I
   datastruct.(sprintf('ENF%d', i)) = sfields{i}
end
The extra reassignment at the end should take no time and no memory at all due to the copy on write nature of matlab.
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