Skipping through text file and extracting data

Hello

I have a dump output from another program. A short example of which is below

ITEM: TIMESTEP

1000

ITEM: BOUNDS

0 10

0 10

0 10

ITEM

id type xs ys zs

1 1 0.1 0.1 0.2

3 1 0.5 0.5 0.4

2 1 0.2 0.3 0.4

it then repeats within the same file for other timesteps. I want it to search for a specific timestep within the file (say 1000), then skip down to 'id type xs ys zs' and save the values xs,ys,zs into a (n,3) array. It would need to stop reading when it detects that the line is no longer numeric.

To me this seems like a simple problem, but it appears that matlaab can only read in full files, as I cannot find a 'skip x lines' function, or 'find value in text file' option. Does matlab keep this behind the scenes and not have it as an option for users?

Jay

Answer 1

[Chirag Gupta]

There is no direct solution for this, but you code it up quite easily:

% num is a vector of interested timesteps
function data = readdump(filename,num)

fid = fopen(filename,'r');

% This will be in for loop:
% for i=1:length(num)
 tline = fgetl(fid);
% call to check num
if(checknum(fid,num,tline)) % reality pass num(i)
    % call function to read data
    % you can use the file structure knowledge to your advantage
    % use textscan to skip lines and read data in the desired format
    disp('Read Data');
else
    % skip lines to the next ITEM (again , you can use textscan    (again if you know the struture of the file and its consistent, then its simpler
    disp('Skipping');
end

data = 0;

function out = checknum(fid,num,tline)

if(strcmp(tline,'ITEM: TIMESTEP'))
  % read next line
  c = textscan(fid,'%d',1);
  if(c{1} == num)
      out = true;
  else
      out = false;
  end
end