extracting rows of data

Hello friends,

I have a txt file with two columns X for voltage and Y for current. I have sweeped the voltage from -1.2 to 1.2 multiple times. I want to write a matlab code where I can seperate rows of data ranging from -1.2 to 1.2 and save it in txt file. That means if the code finds five set of -1.2 to 1.2 sweeps it should extract and create five different txt files.

I tried writing a code but it looks like it is not extracting the data but giving teh same input file.

% Prompt the user to select the input data file

[inputFileName, inputFilePath] = uigetfile('*.txt', 'Select the input data file');

if inputFileName == 0

% User canceled the file selection

disp('File selection canceled. Exiting.');

return;

end

% Load the data from the selected input file

inputFile = fullfile(inputFilePath, inputFileName);

data = load(inputFile);

% Define the range you want to extract

minVoltage = -1.2;

maxVoltage = 1.2;

% Find the indices within the specified range

indices = (data(:, 1) >= minVoltage) & (data(:, 1) <= maxVoltage);

% Extract data within the specified range

outputData = data(indices, :);

% Prompt the user to select where to save the extracted data

[saveFileName, saveFilePath] = uiputfile('*.txt', 'Select where to save the extracted data');

if saveFileName == 0

% User canceled the save file selection

disp('Save file selection canceled. Exiting.');

return;

end

% Create the full path for the output file

outputFile = fullfile(saveFilePath, saveFileName);

% Save the extracted data to the output file

writematrix(outputData, outputFile, 'Delimiter', 'tab');

disp(['Data extracted and saved successfully to ' outputFile]);

Answer 1

[Star Strider]

Try this —

T1 = readtable('07010000002.txt');
T1.Properties.VariableNames = {'V','I'}

T1 = 25025×2 table
       V           I   
    ________    _______

    -0.19667    -3.0823
    -0.19333    -3.0827
    -0.19333    -3.0819
        -0.2    -3.0837
    -0.19667    -3.0819
    -0.19667    -3.0819
    -0.19667     -3.081
        -0.2    -3.0825
    -0.19667    -3.0817
    -0.19667    -3.0815
    -0.19667    -3.0829
        -0.2    -3.0823
    -0.19667    -3.0823
        -0.2    -3.0827
    -0.19667    -3.0823
    -0.19667    -3.0821

minI = min(T1.I)*0.99;
maxI = max(T1.I)*0.99;

minV = min(T1.V)*0.99;
minidx = find((T1.V <= minV) & (T1.I <= minI));
stpmin = find(diff([0; minidx]) > 100);
minidxv = minidx(stpmin)

minidxv = 6×1

4502 6168 7834 9500 11167 12833

maxV = max(T1.V)*0.99;
maxidx = find((T1.V >= maxV) & (T1.I >= maxI));
stpmax = find(diff([0; maxidx]) > 100);
maxidxv = maxidx(stpmax)

maxidxv = 6×1

5496 7162 8827 10494 12160 13826

figure
plot(minidx)
hold on
plot(maxidx)
hold off
grid

figure
tiledlayout(3,2)
for k = 1:numel(minidxv)
    nexttile
    IV{k} = sortrows(T1(minidxv(k):maxidxv(k),:), 1);
    plot(IV{k}.V, IV{k}.I)
    grid
    axis('padded')
    xlabel('V')
    ylabel('I')
    filename = sprintf('VI_%05d_%05d.txt',minidxv(k),maxidxv(k));
    title(strrep(filename,'_','\_'))
    writetable(IV{k},filename)
end

dir('*.txt')                                       % Show Files Have Been Written

07010000002.txt     VI_04502_05496.txt  VI_06168_07162.txt  VI_07834_08827.txt  VI_09500_10494.txt  VI_11167_12160.txt  VI_12833_13826.txt  

.

[Sneha Kandapal]

Thank you this worked.

[Star Strider]

As always, my pleasure!

Answer 2

[dpb]

% % Find the indices within the specified range
% indices = (data(:, 1) >= minVoltage) & (data(:, 1) <= maxVoltage);
% % Extract data within the specified range
% outputData = data(indices, :);

The above will output all of the data within min/max over the entire file; it won't segregate separate sections of the sweep; to do that you would have to find separately the two end points and loop over those taking just the values between each pair.

d=dir('*.txt');
data=readmatrix(d.name);
[min(data(:,1)) min(data(:,1))]

ans = 1×2

-1.2033 -1.2033

i1=find(data(:,1)==-1.2)

i1 =

  0×1 empty double column vector

i2=find(data(:,1)== 1.2)

i2 =

  0×1 empty double column vector

assert(numel(i1)==numel(i2))        % make sure have matching pairs

Excepting, you don't have precisely 1.2V on either end so you'll have to be more flexible in finding starting points...

plot(data(:,1))

Oh. That's not what had imagined--each sweep returns to baseline between next...take a little different tack on finding the breakpoints then...

dV=0.025;
[~,ix1]=findpeaks(-data(:,1),'minPeakHeight',1.2-dV,'minPeakDistance',1000)

ix1 = 10×1

4502 6168 7834 9500 11166 12833 14499 16164 17830 19496

[~,ix2]=findpeaks( data(:,1),'minPeakHeight',1.2-dV,'minPeakDistance',1000)

ix2 = 10×1

5498 7165 8829 10497 12163 13828 15495 17162 18828 20493

assert(numel(ix1)==numel(ix2))
subplot(2,1,1)
plot(data(:,1))
hold on
for i=1:numel(ix1)
  plot(ix1(i),data(ix1(i),1),'*') 
  plot(ix2(i),data(ix2(i),1),'x') 
end
ylim([-1.25 1.25]), xlim([ix1(1)-250 ix2(end)+250])
subplot(2,1,2)
hold on
for i=1:numel(ix1)
  plot(data(ix1(i):ix2(i),1),data(ix1(i):ix2(i),2)) 
end
legend(string(1:numel(ix1)))

Answer 3

[Voss]

inputFile = '07010000002.txt';
data = readmatrix(inputFile);

figure
hold on
plot(data(:,1))

min_idx = find(islocalmin(data(:,1),'MinProminence',0.5,'MinSeparation',1000));
max_idx = find(islocalmax(data(:,1),'MinProminence',0.5,'MinSeparation',1000));

plot([min_idx;max_idx],data([min_idx;max_idx],1),'ro')

% create a separate text files for each sweep (from min_idx to max_idx) section:
for ii = 1:numel(min_idx)
    data_section = data(min_idx(ii):max_idx(ii),:);
    output_file = sprintf('section_%02d.txt',ii);
    writematrix(data_section,output_file);
end

Answer 4

[Sulaymon Eshkabilov]

The answer lies in your original data - see the plot of your data. You are extracting the same data with your logical indexing of indices = (data(:, 1) >= minVoltage) & (data(:, 1) <= maxVoltage); % where your actual data in column 1 for voltage varies only within [-1.2 to 1.2].

data = load('07010000002.txt');
plot(data(:,1), data(:,2), 'b-')
grid minor
xlabel('Voltage')
ylabel('Current')
xlim([-1.22  1.22])