MATLAB: Efficient way to import data

data import table

What is the convenient way to import from a csv file containing numbers and letters for data sorting (like Excel filter function)? Does it matter if I read it as table instead of string arrays?

Best Answer

The most convenient way is typically readtable()

The most efficient way appears to be to use textscan(), according to the timings that people have posted. I have seen one report that in some cases readtable() can be much much slower -- though for my purposes it has always been a reasonable speed.

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MATLAB: Efficient way to import large date sets

Try

    len = 1e5;
    str = '2013-12-10, 00:01:02, 1,2,3,4,5,6,7,8,9,0';
    fid = fopen( 'c:\m\cssm\data_2.txt', 'w' );
    for jj = 1 : len
        fprintf( fid, '%s\n', str );
    end
    fclose( fid );
    tic
    fid = fopen( 'c:\m\cssm\data_2.txt', 'r' );
    cac = textscan( fid, '%s%s%f%f%f%f%f%f%f%f%f%f'             ... 
                       , 'CollectOutput',true, 'Delimiter', ',' );  
    fclose( fid );
    toc
    tic
    buf = cell2mat( cac{1} );
    sdn = datenum( buf, 'yyyy-mm-ddHH:MM:SS' ); 
    toc

I get

    Elapsed time is 0.782288 seconds.
    Elapsed time is 1.648444 seconds.

If you have 1GB extra ram for the data, it will scale nicely.

MATLAB: Matlab Slow Import using Import preview

If you are importing a lot of data that's the same format, you can generate code from the Import Wizard and then use that code to pull in other files. It's in the drop-down menu where you usually accept the import.

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MATLAB: Efficient way to import large date sets

MATLAB: Matlab Slow Import using Import preview

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