How to specify the output type of an fread(fid...) ?

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Ian
Ian 2018 年 11 月 30 日
コメント済み: Ian 2018 年 11 月 30 日
fread(...) lets you specify the data type of the data to be read, but appears to always return the results in a matrix of doubles.
d = fread(fid, nc, 'int16');
K>> whos d
Name Size Bytes Class Attributes
d 46080x1 368640 double
That's not a problem for small data amounts, but I need to read files with 2-4 GB files with int16 data and work with it. Reading the a 4 GB file of int16's (2 billion elements) results in a 16 GB array of doubles, which I then need to convert back to int16's, so effectively temporarily uses 18 GB of memory.
Q: is there any way to specify the output data type, or tell fread to return the data in the same data type that it read from the file?
My current work-around is to preallocate an array of int16's, and read the the file in smaller chunks, converting each chunk from doubles back to int16's.
Anybody got a better solution?

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per isakson
per isakson 2018 年 11 月 30 日
Try this little experiment (based on the first example in the doc)
%%
fid = fopen('nine.bin','w');
fwrite(fid,[1:9]);
fclose(fid);
%%
fid = fopen('nine.bin','r');
num = fread( fid, [1,9], 'uint8=>uint8' );
fclose(fid);
and
>> whos num
Name Size Bytes Class Attributes
num 1x9 9 uint8
  1 件のコメント
Ian
Ian 2018 年 11 月 30 日
Excellent. Thanks. I missed that in the documentation, but indeed it's there if one squints hard enough...

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