How to remove repeated date tick labels - matlab

Question

I'm trying to plot 63 years of monthly data and some labels are repeating (indicated by arrows), illustrated by the following figure:
In order to handle x-labels, I used the following code:
xdate = datenum (datestring2, 'yyyy/mm');
plot (xdate,data1.data(:,4), 'b', xdate,data1.data(:,6),'r', ...
xdate,data1.data(:,8),'k', xdate,data1.data(:,10),'g');
xtic=xdate(1):12:xdate(end);
set(gca,'XTick',xtic);
datetick('x', 'mm/yyyy', 'keepticks');
How can I solve that issue?

Answer 1

You can exploit the carryover feature of datenum():
out = datenum(2000,1:14,1);
Let's verify:
datestr(out)
ans =
01-Jan-2000
01-Feb-2000
01-Mar-2000
01-Apr-2000
01-May-2000
01-Jun-2000
01-Jul-2000
01-Aug-2000
01-Sep-2000
01-Oct-2000
01-Nov-2000
01-Dec-2000
01-Jan-2001
01-Feb-2001
Now set them as Xtick:
set(gca,'Xtick',out)
EDIT: use start end dates
% Provide example initial and final date
in = '20100324';
fi = '20130215';
% Decompose with datevec, count number of months, and skip one month if day > 1
infi = datevec({in,fi},'yyyymmdd');
nmonths = diff(infi(:,1:2))*[12 1]' + infi(1,2);
skipone = infi(1,3) ~= 1;
% Calculate dates
out = datenum(infi(1), (infi(1,2) + skipone):nmonths, 1);

Answer 2

Your expression xtic=xdata(1):12:xdate(end) says that you want a tick every 12 days; often that means you will get two (or even three) repeated months. A quick and dirty solution is
xtic = xdata(1):30:xdate(end);
But that may in some situations skip February, and will be wrong when you run for a large number of months.
To get around this properly, you need to place ticks at the first of every month. A possible way to do that is this:
xdate = datenum(datestring2, 'yyyy/mm');
d1 = datevec(xdate(1)); % [year, month, date, hour, min, sec]
d2 = datevec(xdate(end)+30); % one month past the last data point
nm = ceil((xdate(end) - xdate(1))*12/365); % whole number of months
mv = mod((1:nm) + d1(2) - 2, 12) + 1; % months
yv = d1(1) + floor(((1:nm) + d1(2) - 1)/12); % years
ymdv = [yv' mv' ones(nm,1)]; % year, month, day for each tic
xtic = datenum(ymdv); % will turn this into "the first of every month"
EDIT Oleg Komarov's answer points to a much cleaner way to generate tics at every first of the month - this is using the fact that datenum can cope with months greater than 12. You could probably make the above code a little more compact and cleaner by using that approach (for example, you could leave out the mod operation for mv, and just use d1(1) for the year). But sometimes being explicit about what you are doing isn't a bad thing.