MATLAB function for parsing COMSOL ".txt" data export files into an easily useable struct

comsolread.m

%{
%   COMSOL-MATLAB Parser
%
%   Author: Nicholas McDonald
%   Tested on COMSOL 5.3 for Linux
%
%   This function will parse the COMSOL standard .txt output
%   into a struct that is easily used in MATLAB for data vis.
%
%   It returns a struct "obj" that handles times, parametric
%   studies and geometry of a COMSOL data set.
%
%   Return Struct:
%     obj.meta      - Output file metadata
%     obj.key       - Variable name, unit, time point, parameters
%     obj.raw       - Raw data table by position, key
%       obj.raw.X   - Position data (row)
%       obj.raw.Y   - (Optional)
%       obj.raw.Z   - (Optional)
%       obj.raw.dat - Array of entries (column), corresponding to keys
%
%   Example Usage:
%
%     obj = comsolread("export.txt");
%     t = [obj.key.t];             %Array of Time Data
%     x = [obj.raw.X];                %Array of Position Data
%
%     %Slice all positions, at time = end
%     raw = vertcat(obj.raw.dat); %Raw 2D Data Array
%     val = raw(:, end);
%
%     %Slice all times, position is X = 0
%     val = obj.raw(1).dat
%
%   Warning: This can be slow for large data exports
%}

function obj = comsolread(filename)

  NMF = 7;    %NUM META FIELDS

  fileID = fopen(filename, 'r');          %Open File

  obj.meta = comsolmeta(fileID, NMF);     %Get Metadata Struct (7 Fields)
  obj.meta.Source = filename;             %Add Source file Info
  obj.key = comsolkey(fileID, obj.meta);  %Extract Table Key
  obj.raw = comsolraw(fileID, obj.meta);  %Extract Raw Data

  fclose(fileID);

end

function meta = comsolmeta(fid, metacount)

  key = {}; value = {};

  for i = 1:metacount
    data = strsplit(fgetl(fid), ' ');
    key{i}    = erase(data{2}, ':');
    value{i}  = strcat(data{3});
    for j = 4:length(data);
      value{i} = value{i} + " ";
      value{i} = value{i} + data{j};
    end
  end
  meta = cell2struct(value, key, 2);

  meta.Dimension = str2double(meta.Dimension);
  meta.Nodes = str2double(meta.Nodes);
  meta.Expressions = str2double(meta.Expressions);

end

function [key val] = comsolparam(line)

  if contains(line, "=")
    a = strfind(line, "=");
    key = line(1:a-1);
    val = sscanf(line(a+1:end), "%f");
  end

end

function key = comsolkey(fid, meta)

  g = strsplit(fgetl(fid), " ");

  initial = true;
  i = 2+meta.Dimension;
  while i < length(g)

    keys = {}; vals = {};
    keys{end+1} = 'var';    %Variable Name
    vals{end+1} = g{i+0};
    keys{end+1} = 'unit';   %Unit Expression
    vals{end+1} = g{i+1};

    a = 3;
    while i + a < length(g)+1 && contains(g{i+a}, "=")
      [keys{end+1} vals{end+1}] = comsolparam(g{i+a});
      a = a + 1;
    end

    if initial
      key = cell2struct(vals, keys, 2);
      initial = false;
    else
      key(end+1) = cell2struct(vals, keys, 2);
    end

    i = i + a;

  end
end

function raw = comsolraw(fid, meta)

  initial = true;

  while ~feof(fid)

    tline = fgetl(fid);
    A = strsplit(tline, " ");
    B = struct;

    a = 1;
    if meta.Dimension >= 1
      B.X = str2double(A{a});
      a = a+1;
    end
    if meta.Dimension >= 2
      B.Y = str2double(A{a});
      a = a+1;
    end
    if meta.Dimension >= 3
      B.Z = str2double(A{a});
      a = a+1;
    end

    B.dat = str2double(A(a:end));   % Fill it

    if initial
      raw = B;
      initial = false;
    else
      raw(end+1) = B;
    end

  end
end