How do I change the number of axis ticks while using 'datetick' (Object Oriented Programming, Creating an Application)

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Giacomo Guida 2021-11-4

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评论： Dave B 2021-11-18

I am working on a project that takes the data for the number of COVID-19 Deaths and Cases in all countries/state/regions of the globe, and puts them into a application that shows this information graphically (complete with widgets and all) using MATLAB's App Designer, an acompanying data file, and a classdef .m file to prepare the data. The project and all the widgets work perfectly, however the way I have set up the x-axis lable seems to be in error. The final plot should look something like this:

with monthly x-axis tick lables in the form of (mm/dd). However, when I run my appliation, my output is this (data has changed slightly, so only focus on number of x-axis ticks):

with a quarterly tick seperation instead of a monthly one. I dont want to send the entire code, so I know you wont be able to run the application, but I know that all the code leading to this point is correct I am just strugling with finding a way to alter the number of axis ticks. Below is what I beleive is the necessary code for the situation, if more is needed, please dont heasitate to ask for it and I can send through a less public medium.

This code is at the end of my 'Plot Data' method section (after all of the data has been plotted

    xlim(app.UIAxes,[app.xDATA(1) app.xDATA(end)]); 
    xlim(app.UIAxes,'manual');
    app.UIAxes.YLimMode = 'auto';
    app.UIAxes.YTickMode = 'auto';
    datetick(app.UIAxes,'x','mm/dd',"keeplimits");
    grid(app.UIAxes,'on');
    set(app.UIAxes,'YTickLabel',num2str(get(app.UIAxes,'YTick').','%.f'));
    hold(app.UIAxes,'off');

This is the code in my start-up function that takes the data from my classdef and initiates it.

    globalDATA = DATA('Global');                                            % DATA import      
    app.CountryListBox.Items = (unique(globalDATA.COUNTRY,'stable'));         % Settings for items listed in the Country list box
    app.StateorRegionListBox.Items = (unique(globalDATA.STATE,'stable'));     % Settings for items listed in the State/Region List box
    app.cases_deaths_MATRIX = globalDATA.Cases_Deaths_GLOBAL;
    app.casesVEC = app.cases_deaths_MATRIX(1,:);
    app.deathsVEC = app.cases_deaths_MATRIX(2,:);
    startDATE = datenum(globalDATA.DATE{1});
    endDATE = datenum(globalDATA.DATE{end});
    app.xDATA = linspace(startDATE,endDATE,length(globalDATA.DATE));
    app.averagingWINDOW = app.AveragedofDaysSlider.Value;
    app.StateorRegionListBoxValueChanged;

I appreciate any help that is able to be offered, thank you in advance for your time and assistance.

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Answer 1

Dave B 2021-11-4

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Cool looking app!

One strategy is to set the ticks and then use the keepticks flag:

xdata=datenum(2020,1:4,1);

ydata=rand(1,4);

ax=nexttile;plot(xdata,ydata)

nticks = 4;

xticks(ax,linspace(xdata(1),xdata(end),nticks))

datetick(ax,'x','mm/dd',"keepticks");

ax=nexttile;plot(xdata,ydata)

nticks = 8;

xticks(ax,linspace(xdata(1),xdata(end),nticks))

datetick(ax,'x','mm/dd',"keepticks");

ax=nexttile;plot(xdata,ydata)

nticks = 12;

xticks(ax,linspace(xdata(1),xdata(end),nticks))

datetick(ax,'x','mm/dd',"keepticks");

But if you can use datetime instead of datenum, you might find that options are more flexible (with xtickformat) and you get better ticks:

figure

xdata=datetime(xdata,'ConvertFrom','datenum');

ax=nexttile;plot(xdata,ydata)

nticks = 4;

xticks(ax,linspace(xdata(1),xdata(end),nticks))

ax=nexttile;plot(xdata,ydata)

nticks = 8;

xticks(ax,linspace(xdata(1),xdata(end),nticks))

ax=nexttile;plot(xdata,ydata)

nticks = 12;

xticks(ax,linspace(xdata(1),xdata(end),nticks))

ax=nexttile;plot(xdata,ydata)

nticks = 12;

xticks(ax,linspace(xdata(1),xdata(end),nticks))

xtickformat('MMM dd')

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Dave B 2021-11-10

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To be clear, when you set the ticks manually, they are totally unrelated to the number of data points in your chart. I picked some random data just to show something on the plot, but it was irrelevant.

If you want monthly ticks, set the increment to months. The increment you use for the ticks can be anything you want: days, months, 14 minutes, etc.

Again, all of this is much easier with datetime, because it frees you from concerns about the number of days in each month or leap years or daylight savings time etc.:

datetime(2010,1,1):calmonths(1):datetime(2010,10,1)
ans = 1×10 datetime array
   01-Jan-2010   01-Feb-2010   01-Mar-2010   01-Apr-2010   01-May-2010   01-Jun-2010   01-Jul-2010   01-Aug-2010   01-Sep-2010   01-Oct-2010

Of course, you'll need to decide if you want to place them at the first of each month or the middle or the last. Ticks that are not included in the axes limits are ignored, so it's pretty easy to use the limits or the data itself to decide where the ticks would go:

xdata=datetime(2020,9,13):datetime(2021,5,15); % note that the data are not in monthly increments

ydata=rand(size(xdata));

ax=axes;

plot(ax, xdata, ydata)

lim = ax.XLim;

% Lim will probably be values at the first of the month, but we should make

% sure

first_tick=datetime(lim(1).Year, lim(1).Month, 1);

last_tick=datetime(lim(2).Year, lim(1).Month, 1);

xticks(ax, first_tick:calmonths(1):last_tick)

Giacomo Guida 2021-11-11

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This makes more sense, and thank you for the clarification! I have attempted to alter your given code using my data, and I have gotten it to work except for 2 slight issues. I end up with two seperate sets of overlapping xtick marks. For the data that I am given, the first date is 01/22/20 (making the first month be Jan 2020) and the end date is 01/30/2021 (making the desired last month be Jan 2021). For the lim=ax.XLim, the end limit becomes April 2021, and the the first set of tick marks is, again, a quarterly split. Once it runs through the section of code that ensures the values be the first of each month, I get a second set of overlapping tixk marks that are monthly, and stop at the correct Jan 2021. Any thoughts on how to deal with this issue? Code and figure shown below:

load('covid_data.mat')
date = covid_data(1,3:end);
startdate = date{1};
enddate = date{end};
xdata  = datetime(startdate):datetime(enddate);
% xdata=datetime(2020,9,13):datetime(2021,5,15); % note that the data are not in monthly increments
ydata=rand(size(xdata));
ax=axes;
plot(ax, xdata, ydata)
lim = ax.XLim;
% Lim will probably be values at the first of the month, but we should make
% sure
first_tick=datetime(lim(1).Year, lim(1).Month, 1);
last_tick=datetime(lim(2).Year, lim(1).Month, 1);
xticks(ax, first_tick:calmonths(1):last_tick)

Giacomo Guida 2021-11-18

I was able to successfuly fix the issue. Thank you very much @Dave B! Your assistance was impecable!

Dave B 2021-11-18

@Giacomo Guida - I'm so glad, hope to see your finished app in file exchange!

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How do I change the number of axis ticks while using 'datetick' (Object Oriented Programming, Creating an Application)

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