Matlab: Read in ascii with varying column numbers & different formats - regex

Question

I have been working on a puzzling question that involves reading an ascii file into matlab that contains 2 parts of different formats, the first part also including different column numbers.
MESH2D
MESHNAME "XXX"
E3T 1 1 29 30 1
E4Q 2 2 31 29 1 1
E4Q 3 31 2 3 32 1
...
...
...
ND 120450 5.28760039e+004 7.49260000e+004 8.05500000e+002
ND 120451 5.30560039e+004 7.49260000e+004 6.84126709e+002
ND 120452 5.32360039e+004 7.49260000e+004 6.97750000e+002
ND 120453 5.34010039e+004 7.49110000e+004 7.67000000e+002
NS 1 2 3 4 5 6 7 8 9 10
NS 11 12 13 14 15 16 17 18 19 20
NS 21 22 23 24 25 26 27 -28
BEGPARAMDEF
GM "Mesh"
I am only interested in the lines that contain the triangles and start with E3T/E4Q and the corresponding lines that hold the coordinates of the nodes of the triangles and start with ND. For the triangles (E3T/E4Q lines) I am only interest in the first 4 numbers, therefore I was trying to do something like this:
fileID = fopen(test);
t1 = textscan(fileID, '%s',3);
t2 = textscan(fileID, '%s %d %d %d*[^\n]');
fclose(fileID);
So read in the header to jump to the data and then read the first string and following 4 numbers, then jump to the end of the line and restart. But this does not work. I only get A single line with data and not the rest of the file. Also, I do not know how to treat the second part of the file, which starts at an arbitrary amount of numbers (which I could of course look up manually and feed into matlab, but would prefer matlab to find this change in format automatically).
Do you have any suggestions?
Cheers!

Answer 1

I suggest that you first read all the lines of the file with textscan as strings, and then filter out whatever you need:
fid = fopen(filename, 'r');
C = textscan(fid, '%s', 'delimiter', '');
fclose(fid);
Then parse only the E3T/E4Q/ND lines using regexp:
C = regexp(C, '(\w*)(.*)', 'tokens');
C = cellfun(#(x){x{1}{1}, str2num(x{1}{2})}, C, 'UniformOutput', false);
C = vertcat(C{:});
And then group corresponding E3T/E4Q and ND lines:
idx1 = strcmp(C(:, 1), 'E3T') | strcmp(C(:, 1), 'E4Q');
idx2 = strcmp(C(:, 1), 'ND');
N = max(nnz(idx1), nnz(idx2));
indices = cellfun(#(x)x(1:4), C(idx1, 2), 'UniformOutput', false);
S = struct('tag', [C(idx1, 1); cell(N - nnz(idx1), 1)], ...
'indices', [indices; cell(N - nnz(idx1), 1)], ...
'nodes', [C(idx2, 2); cell(N - nnz(idx2), 1)]);
I named the E3T/E4Q values "indices" and ND values "nodes". The resulting array S contains structs, each having three fields: tag (either E3T or E4Q), indices and nodes. Note that if you have more "indices" than "nodes" or vice versa, the missing values are indicated by an empty matrix.

Answer 2

I know this is not perfect, but if your files are not too big you can do something like this:
fileID = fopen(test,'r');
while ~feof(fileID)
FileLine = fgetl(fileID);
[LineHead,Rem] = strtok(FileLine); % separated string header and numbers
switch LineHead
case 'MESH2D'
% do something here
case 'MESHNAME'
% do something here
case 'E3T'
% parse integer numbers
[Num,NumCount] = sscanf(Rem, '%d');
case 'E4Q'
% parse integer numbers
[Num,NumCount] = sscanf(Rem, '%d');
case 'ND'
% parse integer numbers
[Num,NumCount] = sscanf(Rem, '%d');
% or if you prefer to parse first number separately
[strFirst,strOthers] = strtok(Rem);
FirstInteger = str2num(strFirst);
[Floats,FloatsCount] = sscanf(strOthers, '%g');
% and so on...
end
end
fclose(fileID);
OF course, you have to handle strings starting with MESH2D, MESHNAME, or GM separately