Struggling to plot the data over timestamps!

Hi,

I have data capture with timestamps, I am plotting the data over time stamps, can anyone help as I am struggling to plot it. I pasted the data down below as I reached my limit of sharing files.

Code:

files = ['F:\3-PIV_Experimental_Data\Outlet_110\Data_LaserSheet_D\Data_Head\Data_Raw\Head_Timestamps.xlsx'];
a = readtable(files);
x = a{:,1};
y = a{:,2};
figure()
plot(x,y)

Error:

Error using plot

Invalid data argument.

Error in TimeStamps (line 8)

plot(x,y)

Data:

TimeStamps  Head(mm) 

13:31:39  0 

13:31:49  8.1 

13:31:59  15.3 

13:32:09  24.4 

13:32:19  30.8 

13:32:29  38.3 

13:32:39  44 

13:32:49  50.4 

13:32:59  57.6 

13:33:09  63.4 

13:33:19  68.7 

13:33:29  74.1 

13:33:39  78.9 

13:33:49  83.5 

13:33:59  88.3 

13:34:09  93.1 

13:34:19  97.4 

13:34:29  102.1 

13:34:39  105.7 

13:34:49  109.6 

13:34:59  113.6 

13:35:09  117 

13:35:19  120.3 

13:35:29  123.5 

13:35:39  127 

13:35:49  130.2 

13:35:59  133.3 

13:36:09  136.2 

13:36:19  139.3 

13:36:29  142.4 

13:36:39  145.5 

13:36:49  147.8 

13:36:59  150.5 

13:37:09  153.4 

13:37:19  156 

13:37:29  158.7 

13:37:39  161 

13:37:49  163.4 

13:37:59  166 

13:38:09  168.5 

13:38:19  171.5 

13:38:29  174 

13:38:39  176.8 

13:38:49  179 

13:38:59  181.8 

13:39:09  184.3 

13:39:19  186.9 

13:39:29  189.5 

13:39:40  192.6 

13:39:50  195.2 

13:40:00  197.9 

13:40:10  200.8 

13:40:20  203.1 

13:40:30  206 

13:40:40  209.4 

13:40:50  212 

13:41:00  215.4 

13:41:10  217.8 

13:41:20  221.4 

13:41:30  224.4 

13:41:40  227.3 

13:41:50  230.2 

13:42:00  232.8 

13:42:10  235.9 

13:42:20  238.8 

13:42:30  242 

13:42:40  244.1 

13:42:50  247.2 

13:43:00  250.6 

13:43:10  253.7 

13:43:20  257 

13:43:30  259.6 

13:43:40  262.8 

13:43:50  265.8 

13:44:00  269.2 

13:44:10  272.4 

13:44:20  275.7 

13:44:30  278.5 

13:44:40  281.6 

13:44:50  284.8 

13:45:00  288.3 

13:45:10  291.5 

13:45:20  294.6 

13:45:30  297.5 

13:45:40  300.8 

13:45:50  304.2 

13:46:00  307.1 

13:46:10  309.9 

13:46:20  314 

13:46:30  316.9 

13:46:40  320.5 

13:46:50  323.8 

13:47:00  327.1 

13:47:10  330.5 

13:47:20  334.1 

13:47:30  337.7 

13:47:40  340.6 

13:47:50  344.2 

13:48:00  347.3 

13:48:10  350.9 

13:48:20  354.2 

13:48:30  357.6 

13:48:40  361.3 

13:48:50  364.5 

13:49:00  367.9 

13:49:10  371.2 

13:49:20  374.5 

13:49:30  378.1 

13:49:40  381 

13:49:50  384.1 

13:50:00  387.5 

13:50:10  390.8 

13:50:20  394.1 

13:50:30  397 

13:50:40  399.9 

13:50:50  403.2 

13:51:00  406.3 

13:51:10  409.3 

13:51:20  412.4 

13:51:30  415.5 

13:51:40  418.6 

13:51:50  421.5 

13:52:00  424.6 

13:52:10  428.4 

13:52:20  431.5 

13:52:30  434.1 

13:52:40  437 

13:52:50  440.1 

13:53:00  443 

13:53:10  445.6 

13:53:20  448.3 

13:53:30  451.1 

13:53:40  454.2 

13:53:50  456.8 

13:54:00  459.8 

13:54:10  462.6 

13:54:20  465.2 

13:54:30  468.3 

13:54:40  470.8 

13:54:50  473.6 

13:55:00  476.2 

13:55:10  478.9 

13:55:20  481.7 

13:55:30  484.4 

13:55:40  487.2 

13:55:50  489.7 

13:56:00  492.3 

13:56:10  495.1 

13:56:20  497.8 

13:56:30  500 

13:56:40  502.4 

13:56:50  502.6 

[Jon]

Does the script I provided along with the Excel file I attached run correctly for you? If so then you have to look at what other differences there may be between my Excel file and yours. I am running R2021b.

I see now @Star Strider has also given you some good advice.

Alternatively, reading in from the Excel sheet, just using readtable, as you have done in your origina post gives you serial date number values. You can convert these to datetime array values and plot as follows

files = ['Head_Timestamps.xlsx'];
    a = readtable(files);
    x = a{:,1};
    y = a{:,2};


    % convert timestamp numerical values to datetime array
    t = datetime(x,'ConvertFrom','datenum');
    figure
    plot(t,y)

which gives the following (MATLAB doesn't know what month or year is plotted so it gives Dec31,-1) if this bothers you, it could probably be cleaned up with a little more work

Answer 1

[Star Strider]

I am resisting the temptation to copy all of those, that should be in a text or spreadsheet file and attached here, anyway.

If the time stamps are read in as character arrays (they should be), this should work —

C = {'13:31:39'  0  
     '13:31:49'  8.1  
     '13:31:59'  15.3
     '13:32:09'  24.4 
     '13:32:19'  30.8 
     '13:32:29'  38.3 
     '13:32:39'  44 
     '13:32:49'  50.4 
     '13:32:59'  57.6};

a = table(C(:,1),cell2mat(C(:,2)), 'VariableNames',{'TimeStamps', 'Head(mm)'})          % Replaces The 'readtable' Call

a = 9×2 table
     TimeStamps     Head(mm)
    ____________    ________

    {'13:31:39'}         0  
    {'13:31:49'}       8.1  
    {'13:31:59'}      15.3  
    {'13:32:09'}      24.4  
    {'13:32:19'}      30.8  
    {'13:32:29'}      38.3  
    {'13:32:39'}        44  
    {'13:32:49'}      50.4  
    {'13:32:59'}      57.6  

a.TimeStamps = datetime(a.TimeStamps, 'InputFormat','HH:mm:ss', 'Format','HH:mm:ss')

a = 9×2 table
    TimeStamps    Head(mm)
    __________    ________

     13:31:39          0  
     13:31:49        8.1  
     13:31:59       15.3  
     13:32:09       24.4  
     13:32:19       30.8  
     13:32:29       38.3  
     13:32:39         44  
     13:32:49       50.4  
     13:32:59       57.6  

VN = a.Properties.VariableNames;

figure
plot(a.TimeStamps, a.('Head(mm)'))
grid
xlabel(VN{1})
ylabel(VN{2})

Experiment as necessary to get the desired result.

.

[muhammad choudhry]

hey, thanks for the help! I am getting further error.

Code:

files = ['F:\3-PIV_Experimental_Data\Outlet_110\Data_LaserSheet_D\Data_Head\Data_Raw\Head_Timestamps.xlsx'];
C = readtable(files);
a = table(C(:,1),cell2mat(C(:,2)), 'VariableNames',{'TimeStamps', 'Head(mm)'})   % Replaces The 'readtable' Call
a.TimeStamps = datetime(a.TimeStamps, 'InputFormat','HH:mm:ss', 'Format','HH:mm:ss')
VN = a.Properties.VariableNames;
figure
plot(a.TimeStamps, a.('Head(mm)'))
grid
xlabel(VN{1})
ylabel(VN{2})

Error:

Error using cell2mat (line 42)

Subscripting into a table using one subscript (as in t(i)) or three or more subscripts (as in t(i,j,k)) is not supported. Always

specify a row subscript and a variable subscript, as in t(rows,vars).

Error in TimeStamps (line 5)

a = table(C(:,1),cell2mat(C(:,2)), 'VariableNames',{'TimeStamps', 'Head(mm)'}) % Replaces The 'readtable' Call

>> TimeStamps

Error: File: TimeStamps.m Line: 5 Column: 71

Invalid expression. When calling a function or indexing a variable, use parentheses. Otherwise, check for mismatched delimiters.

[Star Strider]

It is not necessary to construct ‘a’ as I did to create the table, since in your code, the readtable code does that.

Just use this part of my code with your ‘a’ table, so the complete code is now —

files = ['F:\3-PIV_Experimental_Data\Outlet_110\Data_LaserSheet_D\Data_Head\Data_Raw\Head_Timestamps.xlsx'];
a = readtable(files);
a.TimeStamps = datetime(a.TimeStamps, 'InputFormat','HH:mm:ss', 'Format','HH:mm:ss')
VN = a.Properties.VariableNames;

figure
plot(a.TimeStamps, a.('Head(mm)'))
grid
xlabel(VN{1})
ylabel(VN{2})

This assumes that the time stamps are read in as character arrays, not datetime arrays, since the reported error leads me to believe that is the situation. My code converts them to datetime arrays, and thsn plots them.

I cannot test this without the actual file, however it should work, and produce the desired result.

.

[muhammad choudhry]

thank you so much for all the explanations! and helping me out. It worked!

[Jon]

When I made a simple example using the attached .xlsx file and read the data in using (following the OP's example which I was trying to reproduce the problem with)

files = ['Head_Timestamps.xlsx'];
    a = readtable(files);
    x = a{:,1};
    y = a{:,2};

I found that the resulting time values, x, were serial datenumbers (fractions of a 24 hour day). Do you know why they didn't get read in as a character array, as it looks like you expected?

Thanks,

Jon

Answer 2

[Jon]

I copied and pasted your data into an .xlsx file (attached here) and ran your commands (only modified to have the .xlsx file in the local directory)

files = ['Head_Timestamps.xlsx'];
    a = readtable(files);
    x = a{:,1};
    y = a{:,2};
    figure()
    plot(x,y)

and got the following plot, without errors. So I am unable to reproduce your problem. Maybe there some difference in formatting or something like that between my .xlsx file and the one you are using. Please have a look and see if you can make a small self contained example to reproduce the problem.

I'm not sure what you mean by having "reached your limit of sharing files", but you should be able to attach a small .xlsx file as I have here. Please attach a small file that reproduces your problem. Also, I suggest using the code button on the MATLAB answers toolbox to get your code nicely formatted, and to make it easy to cut and paste out of the post.

[muhammad choudhry]

Cannot attach this file because:

• You are limited to 10 daily uploads. If you need to upload additional files, delete one or more files now or wait 24 hours to upload more files.

That's a message appearing. What version of matlab are you using ? I tested again its not working! Why there are numbers in your x-axis instead of timestamps?