MATLAB: How to extract part of the information

This is what i have. (note: originally i have 7 columns but i have only shown just 2 columns for convenience)

'No.' 'Time'

    '1'       '0.000000000' 
    '2'       '0.100209000' 
    '3'       '0.199458000' 
    '4'       '0.299589000' 
    '5'       '0.399856000' 
    '6'       '0.499050000' 
    '7'       '0.599287000' 
    '8'       '0.698449000' 
    '9'       '0.798677000' 
    '10'      '0.898885000' 
      '
    '1000'    '99.00000000'

Here is the code i use to extract

 fid  = fopen('eT1.txt', 'r');
data = textscan(fid, '%d%f%s%s%s%d%s', 'MultipleDelimsAsOne',true, 'HeaderLines',1);
fclose(fid);

But what i want only 1000 values extracted. In that case i need all the 7 columns but till No==1000. how to do that?

Best Answer

Assuming you only want 1000 rows and not just 1000 values (which is not a multiple of 7):

data = textscan(fid, '%d%f%s%s%s%d%s', 1000, 'MultipleDelimsAsOne',true, 'HeaderLines',1);

It's all there in the documentation of textscan (parameter N)

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fmt1='mode%n';
fmt2=['(' repmat('%f',1,3) ')'];
flds={'X','Y','Z'};
fid=fopen(fname,'r');
dat=struct([]);
i=0;
while ~feof(fid)
  i=i+1;
  dat(i).m=cell2mat(textscan(fid,fmt1,1));
  for j=1:length(flds)
    dat(i).(flds{j})=cell2mat(textscan(fid,fmt2,3,'collectoutput',1)).';
  end
end
fid=fclose(fid);

will return a stuct array dat with fields m,_X_,_Y_,_Z_

You will have to find the initial section in the file before using this code snippet (after the fopen of course) by either knowing a priori a 'headerlines' count number or using a loop and fgetl(fid) to read records until find the section wanted.

A test here returned

>> fname='ZA.dat';
>> ZA
>> whos dat
  Name      Size            Bytes  Class     Attributes
    dat       1x5              3392  struct              
>> dat(1)
ans = 
  struct with fields:
      m: 1
      X: [3×3 double]
      Y: [3×3 double]
      Z: [3×3 double]
  >> dat(1).X
  ans =
           0    0.3469    0.1950
      0.3469         0         0
      0.1950         0         0
  >> dat(2).X
  ans =
           0   -0.3469    0.1950
     -0.3469         0         0
      0.1950         0         0
  >>

MATLAB: Subtracting and saving in an array

Based on the text file that you uploaded, I altered my first answer to read all of the columns in your data:

fid  = fopen('temp.txt', 'r');
data = textscan(fid, '%d%f%s%s%s%d%s', 'MultipleDelimsAsOne',true, 'HeaderLines',1);
fclose(fid);
jumps = sum(abs(diff(data{1})>1));
timeD = diff(data{2});

After placing this in a script and running it, I can confirm that it correctly extracts the data from your sample data file:

Note that I altered your text file by removing data row six to provide a jump in the first column, which it seems you want to detect, otherwise it is identical to what you uploaded earlier.

Best Answer

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