How to plot a .txt file when the data is in blocks and each data is separated by space

Hi All,

In the .txt file I have the first block as x axis, the data is not in column i.e. the first value is 1st row (1.0000E-08), second value (1.5850E-08) is second row and last value is last row (1.0000E+01 )

1.0000E-08 1.5850E-08 2.5120E-08 3.9810E-08 6.3100E-08 1.0000E-07 1.5850E-07
2.5120E-07 3.9810E-07 6.3100E-07 1.0000E-06 1.5850E-06 2.5120E-06 3.9810E-06
6.3100E-06 1.0000E-05 1.5850E-05 2.5120E-05 3.9810E-05 6.3100E-05 1.0000E-04
1.5850E-04 2.5120E-04 3.9810E-04 6.3100E-04 1.0000E-03 1.5850E-03 2.5120E-03
3.9810E-03 6.3100E-03 1.0000E-02 1.5850E-02 2.5120E-02 3.9810E-02 6.3100E-02
1.0000E-01 1.5850E-01 2.5120E-01 3.9810E-01 6.3100E-01 1.0000E+00 1.5850E+00
2.5120E+00 3.9810E+00 6.3100E+00 1.0000E+01  

Now the second block is my y axis, and the data is arranged silimarly as above.

0.0000E+00 0.0000E+00 0.0000E+00 0.0000E+00 0.0000E+00 0.0000E+00 0.0000E+00
0.0000E+00 0.0000E+00 0.0000E+00 0.0000E+00 0.0000E+00 0.0000E+00 0.0000E+00
0.0000E+00 0.0000E+00 0.0000E+00 0.0000E+00 0.0000E+00 0.0000E+00 0.0000E+00
0.0000E+00 0.0000E+00 0.0000E+00 0.0000E+00 0.0000E+00 0.0000E+00 0.0000E+00
0.0000E+00 0.0000E+00 0.0000E+00 0.0000E+00 0.0000E+00 0.0000E+00 0.0000E+00
0.0000E+00 0.0000E+00 0.0000E+00 0.0000E+00 0.0000E+00 0.0000E+00 0.0000E+00
0.0000E+00 0.0000E+00 5.7314E+00 0.0000E+00

The file has multiple plot data in it. Therefore, I am trying to first arrange the data in separate coloums and use some coloums for plotting as Y axis value block is repeated twice for each case.

It will be great if someone please give me some direction to start on this.

Thank you in advance for your time and attention.

Answer 1

[Chris]

Wow, that is an inconvenient format.

One option is to use the data import tool--right-click on the text file in matlab and "import data", choose "space" as the delimiter, and highlight everything before importing. Then you can pick your data out of the matrix as needed.

Another option, if you're going to be doing this often, is to import the data as strings using readlines().

data = readlines('Source1_.txt');

Then, in a for loop, split each line using something like

for idx = 1:numel(data)
    temp = readlines(idx).strip.split;
    ...
end

This will give you strings you can analyze. On the first line, for instance,

str2double(temp(1))

tells you the number of data points for the first block.

I can't see how to get the number of blocks in a section, though, so you may have to then look for a line that indicates the end of the section.

Or, just copy/paste things from Excel.

Edit:

The following is incredibly fragile, but it will give you a cell array of the data for this specific file.

data = readlines('Source1_.txt');
dataswitch = false;
alldata = [];
datavect = [];

for idx = 1:numel(data)
    temp = char(data(idx).strip.split);
    if all(size(temp) == [4,2]) || all(size(temp) == [4,3])
        % Get the size of a block
        numpts = str2double(temp(1,:));
    elseif size(temp,2) >= 10 && any(temp(1,[7,8])=='E') 
        % we see scientific notation
        switch dataswitch
            case false
                dataswitch = true;
                datavect = double(string(temp));
            case true
                datavect = [datavect; double(string(temp))];
        end
        if numel(datavect) == numpts % End of block
            alldata = [alldata,{datavect}];
            datavect = [];
            dataswitch = false;
        end

      % On review, the 'else' appears to be redundant
%     else % Not data
%         switch dataswitch
%             case true
%                 % We just passed the end of a block
%                 dataswitch = false;
%                 alldata = [alldata,{datavect}];
%                 datavect = [];
%             case false
%                 % next iteration
%         end
    end
end

Access the first block like alldata{1};

If you want to plot the second and third blocks against the first:

figure
plot(alldata{1},[alldata{2:3}])

or

figure
hold on
plot(alldata{1},alldata{2})
plot(alldata{1},alldata{3})

[Ron]

Hi Chris,

Thank you for your answer.

I tried importing but it is separating the columns where there is space. But all the data in the first block belongs to a column and thje space represents separate row intead of column.

[Chris]

@Ron

I jhave edited my answer with some code that might help you get started.

It will fail if there are more than 999 points in a block, and probably under other conditions not present in this file.

[Ron]

Hi Chris,

Thanks again!!

I am not reading the data from a serial port output. The .txt file is generated from a FORTRAN software and saved in the computer. Therefore, the "readline" is not working for me. What other function can be used in this case. 'Load' can't be used as the data is not arranged in columns.

[Chris]

It's readlines, for text files.

Are you using a version older than 2020b?

[Ron]

Hi Chris,

Thank you very much.

Yes, the issue was on running the program on older version. Running it on the newer version worked fine.

Thank you very for the code.