appending matrices to binary file - recover with fread and reshape?

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Filip 2017-3-9

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https://ww2.mathworks.cn/matlabcentral/answers/328997-appending-matrices-to-binary-file-recover-with-fread-and-reshape

评论： kevin sayed 2021-3-15

Hi!

I need some help on how to recover data from a binary file. I want to store a huge matrix by appending k 1000 x 9000 matrices to a binary file, but I don't know how to recover them in the right order after reading the file using fread and reshape. I want my big matrix to be of size k*1000 x 9000, i.e. the size when concatenating the matrices in the first dimension. Here is what I am doing in principle:

fid = fopen('binFile.bin','a');
for n = 1:k
     data = rand(1000,9000);
     fwrite(fid,data,'double');   
end
bigData = fread(fid,[k*1000*9000],'double');
bigMatrix = reshape(bigData,[k*1000, 9000]);

Thankful for any pointers to solve this!

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Answer 1

Filip 2017-3-10

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https://ww2.mathworks.cn/matlabcentral/answers/328997-appending-matrices-to-binary-file-recover-with-fread-and-reshape#answer_258137

编辑：Filip 2017-3-10

在 MATLAB Online 中打开

I figured it out myself:

By transposing the matrix before writing to file, the matrices are appended as expected. Here is the working script in case anyone else experience the same issue:

fid = fopen('binFile.bin','a');
for n = 1:k
     someData = rand(1000,9000);
       % transpose 
       data = someData';
       fwrite(fid,data,'double');   
  end
% slurp up the file with fread
bigData = fread(fid,[k*1000*9000],'double');
% reshape
bigMatrix = reshape(bigData,[k*1000, 9000]);