I have data under headings with underscore.i e. tce500_a,tce500_b... How can I read data under tce500_c. The '_' is not recotnized and using t500 reads all of them.Thanks

t500_a
0     50
0.5   40

I want to read the data under each heading distinguished by _a,_b,_c, etc.

[Walter Roberson]

I am not clear if you have multiple files, or if you have multiple variables, or if you are using xlsread() and you want to match the rows that have _c as part of their first column, or if you are using readtable and you want to match rows that have _c as part of their first column?

[Marina Evans]

I have one text file which contains multiple headers which identify the data. The data consists of two columns, one is time and the other is concentration measurements. We have repeated experiments, so the header identifies each single set of columns. For example, t500_a contains two columns for the first experiment; t500_b contains two columns for the next experiment, etc. I want to read the entire txt file, find a specific header for the experiment I want, say t500_c, and then read the two columns of data under that specific header (experiment). It is a pretty big file with strings separating the data I want to read for a specific case. Thank you for your help.

[Marina Evans]

Part of my question is how to deal with the underscore symbol. Thanks

Answer 1

[Walter Roberson]

S = fileread('YourFileName.txt');

[headers, block_start] = regexp(S, '^[^\n]*_[^\n]*', 'lineanchors', 'match');

block_bounds = [block_start, length(S)+1];

headers_to_extract = {'t500_c', 'ta719_d'};

num_to_extract = length(headers_to_extract);

extracted_data = cell(num_to_extract, 1);

[tf, blkidx] = ismember(header_to_extract, headers);

for K = 1 : num_to_extract
  if ~tf(K)
    fprintf('Warning: header "%s" not found in file\n', headers_to_extract{K});
  else
    thisidx = blkidx(K);
    thisblock = S( block_bounds(thisidx) : block_bounds(thisidx+1) - 1 );
    extracted_data(K) = textscan(thisblock, '%f %f', 'HeaderLines', 1, 'CombineOutput', 1);  %note rhs is a cell
  end
end

The result will be a cell array, extracted_data, with as many entries as was in the list headers_to_extract, each entry of which is the relevant data from the file. In the case where the header was not found in the file, the entry will be empty. The cells will be in the same order as headers_to_extract