Read values from headers in txt file as parameters, as well as separately reading data matrix from the rest of the file.

Hello all,

If I have a txt file in the format of:

dt 0.001000
tfinal 50.000000
A 6000
B 22.0
C 36.000000
D 9000.000000
E 5.700000
F 15.000000
batch_run from t = 0 to 50 in steps of 0.001 with dt = 0.001
........................................................................
........................................................................
........................................................................
........................................................................
........................................................................
........................................................................

where ..... above represents a (n x m) data matrix.

How would it be best to go about reading the values from the headers (dt, tfinal, A,..,F) and setting them as new variables in my workspace, ignoring the line "batch_run from t = 0 to 50...".

Then in addition to this separately reading just the data matrix, creating a new variable in my workspace where all the headers have been removed and only the matrix remains.

Many thanks.

Answer 1

[Image Analyst]

Obviously there's no built-in reader for that format of a file so you'll have to write your own. Use fgetl() like this:

% Open the file.
fileID = fopen(fullFileName, 'rt');
% Read the first line of the file.
textLine = fgetl(fileID);
while ischar(textLine)
  % Read the remaining lines of the file.
  fprintf('%s\n', textLine);
  % Read the next line.
  textLine = fgetl(fileID);
  % Now parse the line
  if contains(textLine, 'dt ')
  elseif contains(textLine, 'tfinal ', 'IgnoreCase, true)
      etc.
end
% All done reading all lines, so close the file.
fclose(fileID);

Basically you need to recognize when you are on a certain type of line and parse that line appropriately

[tg295]

Thanks for getting back to me.

When I tried this method textLine returns -1. I believe this is because fopen does not open the file correctly as it returns 25 as the fileID.

Please bear with me as I am fairly new to MATLAB.

[Image Analyst]

What is the value of fullFileName? For example 'c:\whatever\myfile.txt'.

And are you absolutely sure a file exists there? And no other program has it open?

[tg295]

'6000_Hz_22.0_mA.txt'

The file exists within the same directory as the matlab script, and no other program has it open.

[tg295]

and when I tried with the full name i.e. 'c:\whatever\6000_Hz_22.0_mA.txt' it did the same thing

[Paolo]

Have you tried my solution?

[tg295]

Paolo, I tried your solution and it did work thanks. Also Image Analyst I realised that the file had been deleted for some reason so had another go and it seems to have worked for the first line 'dt 0.001000', but I didn't know what to include where you had written 'etc' so have only tested it for the first line.

Despite both solutions however, the data matrix I am working with is fairly large and so scanning through the whole dataset takes some time and in the case of Paolo's solution produces some very large structures which are computationally quite heavy. I may just input the values in manually for future datasets unless there is a method that doesn't require scanning through the whole dataset. Thanks a lot for both your help though.

[Image Analyst]

This seems to work with the attached text file I created.

% Open the file.
fullFileName = fullfile(pwd, 'text.txt');
fileID = fopen(fullFileName, 'rt');
% Read the first line of the file.
textLine = strtrim(fgetl(fileID));
while ischar(textLine)
  % Print this line to the command window.
  fprintf('%s\n', textLine);
  % Now parse the line
  if contains(textLine(1:2), 'dt')
    dt = str2double(textLine(4:end))
  elseif contains(textLine(1:6), 'tfinal', 'IgnoreCase', true)
    tfinal = str2double(textLine(8:end))
  elseif contains(textLine(1:2), 'A ', 'IgnoreCase', true)
    A = str2double(textLine(3:end))
  elseif contains(textLine(1:2), 'B ', 'IgnoreCase', true)
    B = str2double(textLine(3:end))
  elseif contains(textLine(1:2), 'C ', 'IgnoreCase', true)
    C = str2double(textLine(3:end))
  elseif contains(textLine(1:2), 'D ', 'IgnoreCase', true)
    D = str2double(textLine(3:end))
  elseif contains(textLine(1:2), 'E ', 'IgnoreCase', true)
    E = str2double(textLine(3:end))
  elseif contains(textLine(1:2), 'F ', 'IgnoreCase', true)
    F = str2double(textLine(3:end))
  elseif contains(textLine, 'batch_run from', 'IgnoreCase', true)
    % Now, after this batch_run line we're expecting 5 lines with 5 numbers per line.
    m = zeros(5, 5); % Preallocate space for speed.
    for row = 1 : 5
      % Read the next line.
      textLine = fgetl(fileID);
      m(row, :) = sscanf(textLine, '%f');
    end
  end
  % Read the next line.
  textLine = fgetl(fileID);
end
% All done reading all lines, so close the file.
fclose(fileID);

[tg295]

Yep works perfectly, thanks so much!