labeling x-axis with cell array

Question

I have been searching various forums for hours but it seems impossible to do a thing in Matlab that's automatic in excel... I used uiimport to import an xls file with into two arrays (? total newbie), one containing dates for my x-axis and the other the values I want to plot.

I have 180 values. The dates are three dates per month, more or less ranging from May 2008 until now, end of March.

Using

plot(mynumbers)

set(gca,'XTickLabel',dates)

only puts dates for May 2008 on my x-axis! where did all the other dates go?

Instead using

plot(mynumbers)

set(gca,'XTick',mynumbers,'XTickLabel',dates)

gives error message "??? Error using ==> set Values must be monotonically increasing."

Please help!

Have you tried sorting mynumbers before setting them as the XTick property? That is, set(gca,'XTick',sort(mynumbers),'XTickLabel',dates). — wakjah
I did the sort but it doesn't work, seems like it lables the axis at the very beginning, but it's impossible to read. — oceanfront
Michael, I'm such a newbie I don't understand the code...I mean, in the example they add 360 and I guess it's because of the sinus function, but what do I add for my values, which are simply the ratios of two stocks (stock A divided by stock B)? — oceanfront

Doresoom Doresoom · Accepted Answer · 2013-04-02T20:15:46

where did all the other dates go?

The answer to your first question is that MATLAB only uses the first N number of strings corresponding to the default N number of tick marks on the x axis.

"??? Error using ==> set Values must be monotonically increasing."

The error is telling you that your date ticks must be evenly spaced. Instead of using dates corresponding to your actual data points, you could grab the x tick values that MATLAB automatically assigned to your graph, translate them to text, and then reassign the dates as x tick labels, like so:

% generate example unevenly spaced date vector
time = [now,now+1,now+25,now+28.5,now+36,now+40,now+51,now+65];
% generate random data points
data = rand(size(time));
% plot time vs data, storing the axes handle in the process
figure;
axH = axes;
plot(axH,time,data)
% get the x-axis tick locations
ticLoc = get(axH,'XTick');
% format tick labels (substitute any date format you wish)
ticLab = cellfun(@(x) datestr(x,'mm/dd'),num2cell(ticLoc),'UniformOutput',false);
% apply tick labels
set(axH,'XTickLabel',ticLab)

MATLAB's built-in function datetick also performs similarly.

However, if you zoom afterwards, you won't have accurate tick labels. So you may want to use datetick2 on the File Exchange.

If you're having trouble converting a cell array of dates from Excel into a numeric array, use:

dateNumeric = cell2mat(cellfun(@datenum,dateStrings,'UniformOutput',false));

labeling x-axis with cell array

2 Answers