why is my plot blank?

readtable ("LOGGER31.xlsx")

Warning: Column headers from the file were modified to make them valid MATLAB identifiers before creating variable names for the table. The original column headers are saved in the VariableDescriptions property.
Set 'VariableNamingRule' to 'preserve' to use the original column headers as table variable names.

ans = 89123×6 table
    x_Mills     x_Stamp             x_Datetime           x_thermResistance    x_thermResistance_1      x_NaN   
    _______    __________    ________________________    _________________    ___________________    __________

       999     1.6766e+09    {'17-Feb-2023 14:48:30'}          23651                 1.49            {0×0 char}
      1998     1.6766e+09    {'2023/2/17 14:48:31'  }          23651                 1.49            {0×0 char}
      3000     1.6766e+09    {'2023/2/17 14:48:32'  }          23651                 1.49            {0×0 char}
      3998     1.6766e+09    {'2023/2/17 14:48:33'  }          23651                 1.49            {0×0 char}
      5000     1.6766e+09    {'2023/2/17 14:48:34'  }          23651                 1.49            {0×0 char}
      5999     1.6766e+09    {'2023/2/17 14:48:35'  }          23651                 1.49            {0×0 char}
      6999     1.6766e+09    {'2023/2/17 14:48:36'  }          23651                 1.49            {0×0 char}
      8000     1.6766e+09    {'2023/2/17 14:48:37'  }          23651                 1.49            {0×0 char}
      8999     1.6766e+09    {'2023/2/17 14:48:38'  }          23541                 1.49            {0×0 char}
      9999     1.6766e+09    {'2023/2/17 14:48:39'  }          23651                 1.49            {0×0 char}
     10998     1.6766e+09    {'2023/2/17 14:48:40'  }          23651                 1.49            {0×0 char}
     11999     1.6766e+09    {'2023/2/17 14:48:41'  }          23651                 1.49            {0×0 char}
     12999     1.6766e+09    {'2023/2/17 14:48:42'  }          23651                 1.49            {0×0 char}
     14000     1.6766e+09    {'2023/2/17 14:48:43'  }          23651                 1.49            {0×0 char}
     14998     1.6766e+09    {'2023/2/17 14:48:44'  }          23651                 1.49            {0×0 char}
     16000     1.6766e+09    {'2023/2/17 14:48:45'  }          23651                 1.49            {0×0 char}

x = LOGGER31(:,"x_Datetime")

Unrecognized function or variable 'LOGGER31'.

y = LOGGER31(:,"x_thermResistance")
plot (x,y)

[Stephen23]

Maybe your data consists only of NaNs, or perhaps you are plotting only one point (which by default has no marker... no idea whay that is the default). In any case, without your data we cannot do much more than guess.

[Walter Roberson]

readtable() does not assign the results to a variable by default.

Answer 1

[Sulaymon Eshkabilov]

It looks like that the whole imported data is not taken for x and y to plot them. See - e.g.:

D = readtable('DATA_A.csv');
x = D.N;
y = D.V;
plot(x, y, 'k-')
grid on
xlabel('N')
ylabel('V')

Answer 2

[Star Strider]

Try something like this —

LOGGER31 = readtable('https://www.mathworks.com/matlabcentral/answers/uploaded_files/1300315/LOGGER31.xlsx', 'VariableNamingRule','preserve')

LOGGER31 = 89123×6 table
    %Mills      %Stamp             %Datetime            %thermResistance    %thermResistance_1       %NaN   
    ______    __________    ________________________    ________________    __________________    __________

      999     1.6766e+09    {'17-Feb-2023 14:48:30'}         23651                 1.49           {0×0 char}
     1998     1.6766e+09    {'2023/2/17 14:48:31'  }         23651                 1.49           {0×0 char}
     3000     1.6766e+09    {'2023/2/17 14:48:32'  }         23651                 1.49           {0×0 char}
     3998     1.6766e+09    {'2023/2/17 14:48:33'  }         23651                 1.49           {0×0 char}
     5000     1.6766e+09    {'2023/2/17 14:48:34'  }         23651                 1.49           {0×0 char}
     5999     1.6766e+09    {'2023/2/17 14:48:35'  }         23651                 1.49           {0×0 char}
     6999     1.6766e+09    {'2023/2/17 14:48:36'  }         23651                 1.49           {0×0 char}
     8000     1.6766e+09    {'2023/2/17 14:48:37'  }         23651                 1.49           {0×0 char}
     8999     1.6766e+09    {'2023/2/17 14:48:38'  }         23541                 1.49           {0×0 char}
     9999     1.6766e+09    {'2023/2/17 14:48:39'  }         23651                 1.49           {0×0 char}
    10998     1.6766e+09    {'2023/2/17 14:48:40'  }         23651                 1.49           {0×0 char}
    11999     1.6766e+09    {'2023/2/17 14:48:41'  }         23651                 1.49           {0×0 char}
    12999     1.6766e+09    {'2023/2/17 14:48:42'  }         23651                 1.49           {0×0 char}
    14000     1.6766e+09    {'2023/2/17 14:48:43'  }         23651                 1.49           {0×0 char}
    14998     1.6766e+09    {'2023/2/17 14:48:44'  }         23651                 1.49           {0×0 char}
    16000     1.6766e+09    {'2023/2/17 14:48:45'  }         23651                 1.49           {0×0 char}

x = LOGGER31.('%Datetime');
x{1} = string(datetime(x(1,1),'Format','yyyy/MM/dd HH:mm:ss'));                                 % First Element Has A Different Format
x = datetime(string(x), 'InputFormat',"yyyy/MM/dd HH:mm:ss", 'Format','yyyy/MM/dd HH:mm:ss');   % Convert All To 'datetime'
LOGGER31.('%Datetime') = x                                                                      % 'LOGGER31' With Consistent '%Datetime'

LOGGER31 = 89123×6 table
    %Mills      %Stamp           %Datetime         %thermResistance    %thermResistance_1       %NaN   
    ______    __________    ___________________    ________________    __________________    __________

      999     1.6766e+09    2023/02/17 14:48:30         23651                 1.49           {0×0 char}
     1998     1.6766e+09    2023/02/17 14:48:31         23651                 1.49           {0×0 char}
     3000     1.6766e+09    2023/02/17 14:48:32         23651                 1.49           {0×0 char}
     3998     1.6766e+09    2023/02/17 14:48:33         23651                 1.49           {0×0 char}
     5000     1.6766e+09    2023/02/17 14:48:34         23651                 1.49           {0×0 char}
     5999     1.6766e+09    2023/02/17 14:48:35         23651                 1.49           {0×0 char}
     6999     1.6766e+09    2023/02/17 14:48:36         23651                 1.49           {0×0 char}
     8000     1.6766e+09    2023/02/17 14:48:37         23651                 1.49           {0×0 char}
     8999     1.6766e+09    2023/02/17 14:48:38         23541                 1.49           {0×0 char}
     9999     1.6766e+09    2023/02/17 14:48:39         23651                 1.49           {0×0 char}
    10998     1.6766e+09    2023/02/17 14:48:40         23651                 1.49           {0×0 char}
    11999     1.6766e+09    2023/02/17 14:48:41         23651                 1.49           {0×0 char}
    12999     1.6766e+09    2023/02/17 14:48:42         23651                 1.49           {0×0 char}
    14000     1.6766e+09    2023/02/17 14:48:43         23651                 1.49           {0×0 char}
    14998     1.6766e+09    2023/02/17 14:48:44         23651                 1.49           {0×0 char}
    16000     1.6766e+09    2023/02/17 14:48:45         23651                 1.49           {0×0 char}

VN = LOGGER31.Properties.VariableNames;

x = LOGGER31.('%Datetime');
y = LOGGER31.('%thermResistance');

figure
plot (x,y)
grid
xlabel(VN{3})
ylabel(VN{4})

The plot was blank because the ‘%Datetime’ values were not converting correctly. The first element converted correctly, however the others were all NaT (‘not a time’), equivalent to NaN for numeric values, since they did not have the same formats as the first element, even though they were valid values, as my code demonstrates.

.