MATLAB: How to sort each line in a text file by the first character in a line

matlab text filesorting lines

how do I get a switch case loop that reads a text file line by line and sorts the lines by the beginning character in each line? I need to use a switch case to account for four different characters. I'm using the fgetl function to read the file line by line so now I just need to figure out how to sort the lines by the beggining character. Once I can sort them I will likely store them in different variables.

Best Answer

The data you posted is a bit difficult to work with, so I created my own version that should work with it. It assumes your data are in a cell array.
Try this: 
C = {'G34  706.0461e-003   823.4578e-003   438.7444e-003   489.7644e-003   276.0251e-003'
     'G34  31.8328e-003   694.8286e-003   381.5585e-003   445.5862e-003   679.7027e-003'
     'R01  276.9230e-003   317.0995e-003   765.5168e-003   646.3130e-003   655.0980e-003'
     'R01  46.1714e-003   950.2220e-003   795.1999e-003   709.3648e-003   162.6117e-003'
     'R01  97.1318e-003    34.4461e-003   186.8726e-003   754.6867e-003   118.9977e-003'};
FC = cellfun(@(x)x(:,1), C);                                        % Get First Letters
[Cu,~,idx] = unique(FC, 'stable');                                  % Unique Letters % Indices
Sorted = accumarray(idx, (1:numel(idx)).', [], @(x){C(x)});         % Separate By First LEtter Into Each Cell Of ‘Sorted’
OutG = Sorted{1}                                                    % Display Result

OutR = Sorted{2}                                                    % Display Result
producing: 
OutG =
  2×1 cell array
    {'G34  706.0461e-003   823.4578e-003   438.7444e-003   489.7644e-003   276.0251e-003'}
    {'G34  31.8328e-003   694.8286e-003   381.5585e-003   445.5862e-003   679.7027e-003' }
OutR =
  3×1 cell array
    {'R01  276.9230e-003   317.0995e-003   765.5168e-003   646.3130e-003   655.0980e-003'}
    {'R01  46.1714e-003   950.2220e-003   795.1999e-003   709.3648e-003   162.6117e-003' }
    {'R01  97.1318e-003    34.4461e-003   186.8726e-003   754.6867e-003   118.9977e-003' }
This should work with your data. It is not restricted to simply those letters you posted, and can work with amy set.
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