MATLAB: Wrong dates on axis when plotting from xlsx file

datesgraphstring

I am not able to plot the correct dates when importing data from an .xlsx file. The year is correct but the months and days are wrong. The first date is supposed to be: 14/09/2018
This is my code:
[Sig, TStr, Raw] = xlsread('EV_F00093.xlsx','Sheet2','A1:D109875');
y=Sig(:,4);
x=Sig(:,2);
y_new=y+693960;
z=datestr(x,'HH:MM:SS');
c=datenum(z,'HH:MM:SS'); % convert date(time) into a number to plot it
b=datestr(y_new,'DD/MM/YYYY'); % convert excel serial dates to matlab serial dates
d=datenum(b,'DD/MM/YYYY'); % convert date into a number to plot it
plot(c,d,'.k'); % plot the data,
hold on;
datetick('x','HH:MM:SS') % give the a xaxis time label ticks..
datetick('y','DD/MM/YYYY') % give the b yaxis time label ticks..
I have attached a screenshot of Sig, y_new, d and the plot.
All help is greatly appreciated.
Best

Best Answer

Do you see, that you use "MM" for minutes and months? The format strings for the date format are case-sensitive.
b=datestr(y_new, 'dd/mm/YYYY');
d=datenum(b, 'dd/mm/YYYY');
The conversion over the string representation and back to a serial date number is indirect. See x2mdate. I've seen several workarounds, e.g.:
y = y + datenum(1900, 1, 1) - 2; % Or -1 ?!
c = fix(y); % date
d = rem(y, 1); % time
Do you have a modern Matlab version? Then the datetime objects are better than datestr.