Import dates from csv files and plot them

Hello there, I am using Matlab 2019a and use app designer and I have problem with importing dates from csv file and plot them from uitable. This is my code

First Button

[filename,path] = uigetfile(...
            {'*.csv', 'Text file CSV (*.csv)'}, 'Load File', 'MultiSelect', 'on');
            onefile = readtable(filename, 'Delimiter', '\t ;', 'MultipleDelimsAsOne', true);
            app.uitable1.Data = onefile;
            setappdata(0,'table',onefile);            

Second Button

T = getappdata(0, 'table');
A = table2cell(T); 
ydata1 = cellfun(@mean,A(:,3)); 
ydata2 = cellfun(@mean,A(:,7));
Times = cellfun(@mean,A(:,2)); 
str = convertCharsToStrings(A(:,1));
DateString = datestr(str); 
DateNumber = datenum(DateString); 
Dates = datetime(DateNumber, 'convertFrom', 'datenum','Format', 'dd.MM.yy HH:mm'); 
xdata = Dates + Times;
plot(app.axes1,xdata,ydata2);

It is doing that that convert the format and make the date March 2nd to February 3rd. I also tried table2timetable but it thinks that the column with dates is text so it doesnot work. So I have table which is in cell array and contains character. How can solve this please?I tried almost everything and look through this FAQs, but I still doesnot found that will helps me.

[Johannes Hougaard]

Hi Sarlota

As far as I can tell from your question, the problem arises in the lines

DateString = datestr(str); 
DateNumber = datenum(DateString); 

As the conversion to DateString is unnecessary and does not hold the right options.

My solution would be to skip the conversion to a datestr and jump right onto the datenum, while setting the FormatIn for the datenum function to match your date format from the .csv

It seems that the correct line is:

DateNumber = datenum(str,'dd-mm-yyyy');

and just keeping the remaining code.

[Sarlota Duskova]

Hello,

Thank you for your quick reply, I also skipped the line with str and take data from table and now it is work.

So I thank you for your help. :)

[Johannes Hougaard]

You're welcome.

I'll post my comment to the 'Answer' section as unfortunately I filled in the wrong place.

If you accept the answer afterwards we'll help clear the backlog of unanswered questions.

Answer 1

[Johannes Hougaard]

Hi Sarlota

As far as I can tell from your question, the problem arises in the lines

DateString = datestr(str); 
DateNumber = datenum(DateString); 

As the conversion to DateString is unnecessary and does not hold the right options.

My solution would be to skip the conversion to a datestr and jump right onto the datenum, while setting the FormatIn for the datenum function to match your date format from the .csv

It seems that the correct line is:

DateNumber = datenum(str,'dd-mm-yyyy');

and just keeping the remaining code.

Answer 2

[Peter Perkins]

Sarlota, I recommend that you use datetime, and not use datenum or datestr at all. Especially do not do this

DateString = datestr(str); 
DateNumber = datenum(DateString); 
Dates = datetime(DateNumber, 'convertFrom', 'datenum','Format', 'dd.MM.yy HH:mm'); 

Just convert the text to datetime directly.

But there are some very funny things in your code and your file. You are using multiple delimiters in a file that is clearly semicolon delimited. And the file appears to have either one too many headers, or one too few data columns. And the date/time format you are using does not math what's i the file. You code is very complicated as a result - I think you are making you life too difficult. Let's assume the file is missing a column. I added a semicolon at the end of each data line, equivalent to having an empty field for the last column n the file. (Or maybe I should have deleted the 'current' in the header; I can't tell.) In your MATLAB release, try this

>> T = readtable('matlab.csv', 'Delimiter', ';')
T =
  7×9 table
                 time                 current      avg        min        max      spctemp    wlencomp    ledpower    event
    ______________________________    _______    _______    _______    _______    _______    ________    ________    _____
    {'02-03-2020 14:25:25.468972'}    -92.368     -92.33    -92.382    -92.266     24.56        0         25000       NaN 
    {'02-03-2020 14:25:29.470035'}    -92.325    -92.334    -92.398    -92.279     24.56        0         25000       NaN 
    {'02-03-2020 14:25:33.467210'}    -92.361    -92.338    -92.379    -92.279     24.56        0         25000       NaN 
    {'02-03-2020 14:25:37.477145'}    -92.339    -92.354    -92.398    -92.296     24.56        0         25000       NaN 
    {'02-03-2020 14:25:41.475953'}    -92.348     -92.38    -92.437    -92.331     24.56        0         25000       NaN 
    {'02-03-2020 14:25:45.478137'}     -92.36    -92.398    -92.454    -92.347     24.56        0         25000       NaN 
    {'02-03-2020 14:25:49.475570'}    -92.425    -92.386    -92.434    -92.333     24.56        0         25000       NaN 
>> T.time = datetime(T.time,'Format','dd-MM-uuuu HH:mm:ss.SSSSSS')
T =
  7×9 table
               time               current      avg        min        max      spctemp    wlencomp    ledpower    event
    __________________________    _______    _______    _______    _______    _______    ________    ________    _____
    02-03-2020 14:25:25.468972    -92.368     -92.33    -92.382    -92.266     24.56        0         25000       NaN 
    02-03-2020 14:25:29.470035    -92.325    -92.334    -92.398    -92.279     24.56        0         25000       NaN 
    02-03-2020 14:25:33.467210    -92.361    -92.338    -92.379    -92.279     24.56        0         25000       NaN 
    02-03-2020 14:25:37.477145    -92.339    -92.354    -92.398    -92.296     24.56        0         25000       NaN 
    02-03-2020 14:25:41.475953    -92.348     -92.38    -92.437    -92.331     24.56        0         25000       NaN 
    02-03-2020 14:25:45.478137     -92.36    -92.398    -92.454    -92.347     24.56        0         25000       NaN 
    02-03-2020 14:25:49.475570    -92.425    -92.386    -92.434    -92.333     24.56        0         25000       NaN 
>> TT = table2timetable(T)
TT =
  7×8 timetable
               time               current      avg        min        max      spctemp    wlencomp    ledpower    event
    __________________________    _______    _______    _______    _______    _______    ________    ________    _____
    02-03-2020 14:25:25.468972    -92.368     -92.33    -92.382    -92.266     24.56        0         25000       NaN 
    02-03-2020 14:25:29.470035    -92.325    -92.334    -92.398    -92.279     24.56        0         25000       NaN 
    02-03-2020 14:25:33.467210    -92.361    -92.338    -92.379    -92.279     24.56        0         25000       NaN 
    02-03-2020 14:25:37.477145    -92.339    -92.354    -92.398    -92.296     24.56        0         25000       NaN 
    02-03-2020 14:25:41.475953    -92.348     -92.38    -92.437    -92.331     24.56        0         25000       NaN 
    02-03-2020 14:25:45.478137     -92.36    -92.398    -92.454    -92.347     24.56        0         25000       NaN 
    02-03-2020 14:25:49.475570    -92.425    -92.386    -92.434    -92.333     24.56        0         25000       NaN 
 

Your code does not seem to match what's in your file at all; all those lines involving cellfun in particular seem to not make any sense when I run it. But I would think that all you need at this point is

    >> plot(TT.time,TT.current)

[Sarlota Duskova]

Hello, I used this delimiter '\t ;' because I had error and error sayed I must used that delimiter and when I used it, error disappeared. Then I did not know what to do with date and time so I converted table into cell so that is the reason why I used cellfun. I am a beginner so I need to learn a lot and I am trying some stuff you can see it above and then it works but yeah your sollution is much more easier I dont know why I dont do that before. I spent a lot of time to figure out how to do it, and I did my stupid sollution you can see above. So thank you that you looked at it and help me to see that the solution it can be much more easier.