alternatives to putting multiple placeholders

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ily
ily 2012-3-13
I have an 1000000*8 matrix which I am trying to output to a text file.
fprintf(fid, '\n%12d %12d %12d %12d %12d %12d %12d %12d', P(:,1:8)')
If the matrix had more columns I would be writing the same placeholder (%12d) many more times. Is there a more efficient way to copy a large matrix to a text file preserving the rows and columns, possibly by writing the necessary placeholder just once.

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回答（2 个）

Walter Roberson
Walter Roberson 2012-3-13
No there is not.
You can, however, pre-calculate the format as a string and pass the string in to the call.
numcols = 8;
fmt = [ '\n', repmat('%12d ', 1, numcols) ];
fprintf(fid, fmt, P(:,1:8).');
Jacob Halbrooks
Jacob Halbrooks 2012-3-13
Since all of your data has the same format, you can let FPRINTF repeat the format specifier over all of your data. Here is an example of doing that:
data = rand(5,10);
for rInd = 1:size(data,1)
fprintf('\n');
fprintf('%12d ',data(rInd,:));
end
If your data is not regular enough for this, another approach would be to use REPMAT to dynamically create the format specifier for your data. I wrote an example of that here.

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