MATLAB: Different Results When Using “textscan” vs “fgetl” in MAC

MATLAB

Hi, I have a MATLAB function that processes a file and spits out a [x,y] array. The files are generated with a malformed empty line header because it has "0A0D" while the rest of the file uses "0A".

I'm using "HeaderLines" option in 'textscan' to skip lines. The number of lines calculated by 'fgetl' is correct. However 'textscan' misinterprets the number of lines in the header and skips the wrong number of lines.

How do I change the code to exclude the header consistently. Both files should return 512×1 double array, however one only returns 511×1. I cannot control what is written or how its written in the .txt files. One file has "0A0A" the other file has "0A0D". "0A0D" is supposed to be counted as 2 separate lines.

Best Answer

When a file is opened in vim and Sublime Text on Mac, there is no extra header line. However, the MATLAB Editor does display an extra header line. This is probably what is throwing off the detection code. 'fgetl' and 'textscan' are interpreting the number of header lines differently.

Two workarounds exist:

1. You can use the following call for "textscan" function:

>> dataset = textscan(fid, '%f %f', 'HeaderLines', skipLines, 'CollectOutput', 1, 'EndOfLine', '\r\n');

2. Use "readmatrix" function instead:

dataset = readmatrix(filename);
x = dataset (:,1); 
y = dataset (:,2);

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As mentioned in the documentation of 'textread' for MATLAB, it is recommended to avoid using 'textread' by using 'textscan' instead. The issue seen can be resolved by using 'textscan' instead of 'textread'. Please refer to the attached demo script. The only difference between the scripts is, the attached script uses 'textscan' to read from the file instead of 'textread'.

MATLAB: Does the Import Data wizard not behave as expected when I import files with multiple header rows in MATLAB 7.5 (R2007b)

There is, in general no reason to suppose that headerlines have the same number of delimiters as the data. If the last line has the same number of delimiters, it is treated as column headers. However previous lines usually have very little to do with the data, so they are simply read in as single strings.

To work around this issue, you can use the TEXTSCAN function. The code below illustrates how to do this on the example file given above.

clear all; clc;
fid = fopen('exampledata.txt'); % open file
firstRow = textscan(fid, '%s', 3, 'Delimiter', ','); % read first row of headers
firstRow{1}'
secondRow = textscan(fid, '%s', 3, 'Delimiter', ','); % read second row of headers
secondRow{1}'
temp = textscan(fid, '%n', 3, 'Delimiter', ','); % try to read first line of data
dataRow = 0; % set the number of data lines found so far
while ~isempty(temp{1}) % if the line just read is not empty
      dataRow = dataRow + 1; % increment the number of data lines found
      data(dataRow,:) = temp{1}'; % copy data from line to data matrix
      temp = textscan(fid, '%n', 3, 'Delimiter', ','); % try to read next line of data
end
data
fclose(fid); % close file

Best Answer

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