MATLAB: Reading full column at a time from a text file

columns from text fileiterating over cell arrays

Hi, I am new to Matlab. I have a text file that looks something like this:

1 2 3
4 5 6
7 8 9

I need to add each column separately before I do something with the result. So I need three variables such that

c1 = sum of 1+4+7
c2 = sum of 2+5+8
c3= sum of 3+6+9.

I am reading the text file using using two methods (just trying to see which is better) but they both give me a cell array that reads A = {1, 2, 3, 4, …}. Here's my code, I appreciate your help.

file_length = 40;
w = [3 -1.5 -2]
entry = [];
fileID = fopen('training_inputs1.txt', 'r');
formatSpec = '%f';
A2 = fscanf(fileID, formatSpec)
A = textscan(fileID, formatSpec);
%r1 = A2(:,1),
for i = A2 %1:file_length
    disp(i(:))
      %value = sprintf(formatspec, i)
      %i2 = i + 1;
      %i3 = i + 3;
      %Y2 = w(2) * i2
      %Y3 = w(3) * i3
  end
  %Y = Y1 + Y2 + Y3
  fclose(fileID);

Best Answer

We do not recommend that you process one column at a time. Read in all of the columns into a 2D array, and use sum() on that 2D array: the result will be a row vector with one total per column. You do not need different variables for each column: just index the vector.

Related Solutions

MATLAB: How to delete the first 2 rows (Headers) of a txt file

Well, once you've got the right content in memory, then just rewrite the file. But, specifically on that has some bearing on the content for easy ways.

But, if that is the only thing you care to do, then the simplest irrespective of what the file content is, is probably

fidi=fopen('oldfile.txt','r');
fido=fopen('newfile.txt','w');
headerlines=2;
for i=1:headerlines,fgetl(fidi);end       % skip the desired number
buf=fread(fidi,'*char');                  % suck up the rest as image
fwrite(fido,buf)                          % and spit it out verbatim
fclose('all')                             % done
%delete('oldfile.txt')                    % optionally remove the original keeping new
%movefile('newfile.txt','oldfile.txt')    % optionally rename new to old (only new left as oldfile name)

MATLAB: Reading big textfile with textscan

Solution One

You do not need to delete the first ten rows from the file, because textscan has an option to ignore header lines, so you can use this instead:

Out = textscan(....,'HeaderLines',10);

To read 1280 columns of data you need to define this in the format string, so the final code could be something like this:

fmt = repmat('%f',1,1280);
fid = fopen('textfile.txt','rt')
out = textscan(fid, fmt, 'Delimiter',',', 'HeaderLines',10);
fclose(fid);

Solution Two

If the data in the matrix is all numeric (note the header lines do not need to be) then you could use the much simpler dlmread instead, something a bit like this:

out = dlmread('textfile.txt',',',10,0);

Examples

% textscan
fmt = repmat('%f',1,5);
fid = fopen('temp.txt','rt');
out_txt = textscan(fid, fmt, 'Delimiter',',', 'HeaderLines',3);
fclose(fid);
out_txt = cell2mat(out_txt)
% dlmread
out_dlm = dlmread('temp.txt',',',3,0)

display this in the command window:

out_txt =
     0     1     2     3     4
     5     6     7     8     9
out_dlm =
     0     1     2     3     4
     5     6     7     8     9

The sample text file that I used is attached here:

Best Answer

Related Solutions

MATLAB: How to delete the first 2 rows (Headers) of a txt file

MATLAB: Reading big textfile with textscan

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