How to Put datetime into numeric axis

Hi all,

So I recently wrote a script that can dynamically change x and y axes' data. However, I cannot find a way to plot Date on x-axis.

I use the following way to change the data on axes: (suppose p is the plot line object handle, and somedata is the data I want to show on the axis)

p.XData=somedata;

Everything worked fine if somedata is switching between different double vectors. But if I want to plot date information on x axis, ie. somedata is a datetime vector, then I will get an error saying that the XData must be numeric vector.

I identified the problem to be that the XAxis property of p.Parent (an axes object) is a NumericRuler object, while in order to plot datetime information, it needs to be DatetimeRuler. However, I cannot find a way to change that XAxis property. I cannot find a command that enables me to create DatetimeRuler to replace the NumericRuler.

Can somebody help me with this issue? Thank you very much!

[Walter Roberson]

It is possible to take an existing DatetimeRuler and use it to replace the XRuler of an existing axes, such as

firstax.XRuler = secondax.XRuler

but this leaves kind of a strange state, and deleting the source axes secondax can cause the firstax.XRuler to become empty.

[Heyuan Huang]

Yep, I have tried that. Creating an empty and invisible figure. Then plot a datetime point, extract the datetimeruler and replace the one in real plot. Since I don't want to accumulate many figure objects, I delete each one after copying the ruler object. But then, as you said, the one I copied also gets deleted. So I was going to use the copyobj, but I am wondering if there is any other easy way around this.

Answer 1

[Walter Roberson]

See https://www.mathworks.com/matlabcentral/answers/395868-convert-x-axis-values-to-datetime#answer_316068

[Ted Shultz]

from Walter's link, here is what i came up wtih:

ruler2num is the function you need. it convets from the axis ruler to the axis number. Basicaly you setup a plot wtih datetime on the x axis, and then you can use imagesc to plot using the numeric values that corispond to your datetimes.

 y=[3 7]; % just random number of y axis example
 x=[datetime, datetime+days(5)]; % will plot image from now to five days from now
 A = imread('ngc6543a.jpg'); % this is the image we will use
 h1= plot(x,zeros(size(x))); % make a random plot with time as the x axis (will delete this in a second)
 hold on
 ax1 = gca; % get the current axis
 h2= imagesc(ruler2num(x, ax1.XAxis),y,A); % use ruler2num() to plot this at the location we want
 delete(h1); % delete this line we made before

[Walter Roberson]

Thanks, Ted.