skip data when reading binary
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I have a binary data file, and I am reading it as such.
fileID = fopen('2016.06.27_15.12.07_1.A.bin');
SDDdata = fread(fileID, 1E6, 'uint16' , 'ieee-le');
fclose all;
However, I want to skip every other data point, or every 3, etc. As the file is incredibly large and I want to to some testing with ignoring data. Looking up the fread command I can see there is a skip options, but I could not get it to work for this? It seemed to do nothing?
2 个评论
James Tursa
2016-7-1
Please show the code you are using for skipping. Are you sure you are inputting the number of bytes to skip and not the number of values?
Walter Roberson
2016-7-1
Good point about it being in bytes .
回答（1 个）
Walter Roberson
2016-7-1
In R2016b I tested by writing out uint8(0:255) repeatedly, and then doing several tests
bytes = uint8(0:255);
fid = fopen('testfread.bin', 'w');
for K = 1 : 4096; fwrite(fid, bytes, 'uint8'); end
fclose(fid);
fid = fopen"testfread.bin', 'r');
skip = 0; frewind(fid); data0 = fread(fid, [1 100], 'uint8', skip, 'ieee-le')
skip = 1; frewind(fid); data1 = fread(fid, [1 100], 'uint8', skip, 'ieee-le')
skip = 2; frewind(fid); data2 = fread(fid, [1 100], 'uint8', skip, 'ieee-le')
fclose(fid)
The output was exactly what I expected: first consecutive bytes [0 1 2 3 ...] for skip 0, then every second byte [0 2 4 6 ...] for skip 1, then every third byte [0 3 6 9 ...] for skip 2. Skip seems to work correctly on my system.
2 个评论
James Tursa
2016-7-1
Worked for me too, which is why I want OP to post the exact code being used.
Image Analyst
2016-7-1
Why didn't you try it for uint16? for completeness, I do that below:
% Create sample data file.
bytes = uint16(0:255);
fid = fopen('testfread.bin', 'w');
for K = 1 : 4096; fwrite(fid, bytes, 'uint16'); end
fclose(fid);
% Read it back in.
fid = fopen('testfread.bin', 'r');
numbersToSkip = 0;
bytesToSkip = numbersToSkip * 2; % Multiply by 2 for uint16, which is 2 bytes
frewind(fid);
data0 = fread(fid, [1 100], 'uint16', bytesToSkip, 'ieee-le')
numbersToSkip = 1;
bytesToSkip = numbersToSkip * 2; % Multiply by 2 for uint16, which is 2 bytes
frewind(fid);
data1 = fread(fid, [1 100], 'uint16', bytesToSkip, 'ieee-le')
numbersToSkip = 2;
bytesToSkip = numbersToSkip * 2; % Multiply by 2 for uint16, which is 2 bytes
frewind(fid);
data2 = fread(fid, [1 100], 'uint16', bytesToSkip, 'ieee-le')
fclose(fid)
It's a little bit trickier since you have to multiply the number to skip by 2 since there are two bytes in a uint16 number.
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2016-7-1
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