Struggling to plot the data over timestamps!

Question

muhammad choudhry 2022-1-7

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1624300-struggling-to-plot-the-data-over-timestamps

评论： Jon 2022-1-7

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) 
31:39  0 
31:49  8.1 
31:59  15.3 
32:09  24.4 
32:19  30.8 
32:29  38.3 
32:39  44 
32:49  50.4 
32:59  57.6 
33:09  63.4 
33:19  68.7 
33:29  74.1 
33:39  78.9 
33:49  83.5 
33:59  88.3 
34:09  93.1 
34:19  97.4 
34:29  102.1 
34:39  105.7 
34:49  109.6 
34:59  113.6 
35:09  117 
35:19  120.3 
35:29  123.5 
35:39  127 
35:49  130.2 
35:59  133.3 
36:09  136.2 
36:19  139.3 
36:29  142.4 
36:39  145.5 
36:49  147.8 
36:59  150.5 
37:09  153.4 
37:19  156 
37:29  158.7 
37:39  161 
37:49  163.4 
37:59  166 
38:09  168.5 
38:19  171.5 
38:29  174 
38:39  176.8 
38:49  179 
38:59  181.8 
39:09  184.3 
39:19  186.9 
39:29  189.5 
39:40  192.6 
39:50  195.2 
40:00  197.9 
40:10  200.8 
40:20  203.1 
40:30  206 
40:40  209.4 
40:50  212 
41:00  215.4 
41:10  217.8 
41:20  221.4 
41:30  224.4 
41:40  227.3 
41:50  230.2 
42:00  232.8 
42:10  235.9 
42:20  238.8 
42:30  242 
42:40  244.1 
42:50  247.2 
43:00  250.6 
43:10  253.7 
43:20  257 
43:30  259.6 
43:40  262.8 
43:50  265.8 
44:00  269.2 
44:10  272.4 
44:20  275.7 
44:30  278.5 
44:40  281.6 
44:50  284.8 
45:00  288.3 
45:10  291.5 
45:20  294.6 
45:30  297.5 
45:40  300.8 
45:50  304.2 
46:00  307.1 
46:10  309.9 
46:20  314 
46:30  316.9 
46:40  320.5 
46:50  323.8 
47:00  327.1 
47:10  330.5 
47:20  334.1 
47:30  337.7 
47:40  340.6 
47:50  344.2 
48:00  347.3 
48:10  350.9 
48:20  354.2 
48:30  357.6 
48:40  361.3 
48:50  364.5 
49:00  367.9 
49:10  371.2 
49:20  374.5 
49:30  378.1 
49:40  381 
49:50  384.1 
50:00  387.5 
50:10  390.8 
50:20  394.1 
50:30  397 
50:40  399.9 
50:50  403.2 
51:00  406.3 
51:10  409.3 
51:20  412.4 
51:30  415.5 
51:40  418.6 
51:50  421.5 
52:00  424.6 
52:10  428.4 
52:20  431.5 
52:30  434.1 
52:40  437 
52:50  440.1 
53:00  443 
53:10  445.6 
53:20  448.3 
53:30  451.1 
53:40  454.2 
53:50  456.8 
54:00  459.8 
54:10  462.6 
54:20  465.2 
54:30  468.3 
54:40  470.8 
54:50  473.6 
55:00  476.2 
55:10  478.9 
55:20  481.7 
55:30  484.4 
55:40  487.2 
55:50  489.7 
56:00  492.3 
56:10  495.1 
56:20  497.8 
56:30  500 
56:40  502.4 
56:50  502.6 

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Jon 2022-1-7

编辑：Jon 2022-1-7

在 MATLAB Online 中打开

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

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Answer 1

Star Strider 2022-1-7

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1624300-struggling-to-plot-the-data-over-timestamps#answer_870185

在 MATLAB Online 中打开

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.

.

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muhammad choudhry 2022-1-7

编辑：Walter Roberson 2022-1-7

在 MATLAB Online 中打开

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.

muhammad choudhry 2022-1-7

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

Jon 2022-1-7

在 MATLAB Online 中打开

Head_Timestamps.xlsx

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

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Answer 2

Jon 2022-1-7

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链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1624300-struggling-to-plot-the-data-over-timestamps#answer_870195

在 MATLAB Online 中打开

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.

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muhammad choudhry 2022-1-7

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?

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