MATLAB: How to read in a text file and sort it by a column

reading text filesorting

I have a file which I am trying to read and then sort by column A and then by column C. The text file is attached and has 3 columns. This is what I have tried but it will not let me use the sort function after reading it in this way:

function data = ResultsScript(filename)
    fid = fopen(filename);
    data = textscan(fid, '%s %f %f');
    fclose(fid);
end

Then I call this function and try to sort it using:

fileName = 'Example.txt';
A = ResultsScript(fileName);
sortrows(A,[1,3]);

Running this gives the following error message:

??? Index exceeds matrix dimensions.
Error in ==> sortrows>sort_cell_back_to_front at 133
          ndx = ndx(ind);
Error in ==> sortrows at 90
      ndx = sort_cell_back_to_front(x_sub, col);
Error in ==> GetResults at 3
sortrows(A,[1,3]);

Any help is greatly appreciated.

Best Answer

Dear Aaron, the problem here is that function "textscan" output data in the form of cell array which you must convert first into a matrix before using "sortrows" function because "sortrows" only accept vector or matrix data. So after converting it to proper form you can apply "sortrows". Also don't use "%s" to read values of double type instead use "%f" or better "%n". Following is the corrected code for this purpose:

fid = fopen(filename);
cell_data = textscan(fid, '%n %n %n');
fclose(fid);
matrix_data = [cell_data{:}];

After this you can apply:

sorted_data = sortrows(matrix_data, [1 3]);

Related Solutions

MATLAB: Reading big textfile with textscan

Solution One

You do not need to delete the first ten rows from the file, because textscan has an option to ignore header lines, so you can use this instead:

Out = textscan(....,'HeaderLines',10);

To read 1280 columns of data you need to define this in the format string, so the final code could be something like this:

fmt = repmat('%f',1,1280);
fid = fopen('textfile.txt','rt')
out = textscan(fid, fmt, 'Delimiter',',', 'HeaderLines',10);
fclose(fid);

Solution Two

If the data in the matrix is all numeric (note the header lines do not need to be) then you could use the much simpler dlmread instead, something a bit like this:

out = dlmread('textfile.txt',',',10,0);

Examples

% textscan
fmt = repmat('%f',1,5);
fid = fopen('temp.txt','rt');
out_txt = textscan(fid, fmt, 'Delimiter',',', 'HeaderLines',3);
fclose(fid);
out_txt = cell2mat(out_txt)
% dlmread
out_dlm = dlmread('temp.txt',',',3,0)

display this in the command window:

out_txt =
     0     1     2     3     4
     5     6     7     8     9
out_dlm =
     0     1     2     3     4
     5     6     7     8     9

The sample text file that I used is attached here:

MATLAB: How to sort data once it is read into matlab

The first column of data is a cell array of strings, whereas columns 2 and 3 are numeric arrays. You cannot concatenate them without performing first a conversion. You can also convert numeric arrays to cell arrays and have both strings and numbers in a large cell array. E.g.

 matrix_data = [data{1}, num2cell(data{2}), num2cell(data{3})] ;

 matrix_data = [data{1}, num2cell([data{2:3}])] ;

that you can then sort:

 >> sort_data = sortrows(matrix_data, [1,3]) 
 sort_data = 
    'A88888888888888888880011'    [-65]    [ 1]
    'A88888888888888888880011'    [-52]    [ 2]
    'A88888888888888888880011'    [-64]    [ 3]
    'A88888888888888888880011'    [-52]    [ 4]
    'A88888888888888888880011'    [-57]    [ 5]
    'A88888888888888888880011'    [-65]    [ 6]
    'A88888888888888888880011'    [-57]    [ 7]
    'A88888888888888888880011'    [-55]    [ 8]
    'A88888888888888888880012'    [-66]    [ 9]
    'A88888888888888888880012'    [-52]    [10]
    'A88888888888888888880012'    [-68]    [11]
    'A88888888888888888880012'    [-64]    [12]
    'A88888888888888888880012'    [-44]    [13]
    'A88888888888888888880012'    [-64]    [14]
    'A88888888888888888880012'    [-40]    [15]
    'A88888888888888888880012'    [-51]    [16]
    'A88888888888888888880013'    [-55]    [17]
    'A88888888888888888880013'    [-57]    [18]
    'A88888888888888888880013'    [-49]    [19]
    'A88888888888888888880013'    [-47]    [20]
    'A88888888888888888880013'    [-64]    [21]
    'A88888888888888888880013'    [-60]    [22]
    'A88888888888888888880013'    [-67]    [23]
    'A88888888888888888880013'    [-61]    [24]

Best Answer

Related Solutions

MATLAB: Reading big textfile with textscan

MATLAB: How to sort data once it is read into matlab

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