Drawing the top axis (box) line

Question

I have a plot with two lines and two different x-axis (different data units), which I plot like the following.

My problem is that I would like to draw the top line of the box black as well (horizontally), and not leave it "open" like it is. It would be great if the line had the x-axis ticks as well, same as the bottom horizontal axis line.

Obviously, grid on doesn't work, because it draws the y1-axis ticks on the right and the y2-axis ticks on the left, which I don't want.

Also, I think in Matlab 2014, this worked: set(ax(2),'XAxisLocation','top','XTickLabel',[]); but it doesn't anymore in Matlab 2015a.

Here's the example:

figure(1);
x = [0, 1, 2, 3];
y_1 = [3, 2, 1.5, 1];
y_2 = [0, 0.5, 0.7, 0.9];
parula_blue = [0, 0.447, 0.741]; parula_red = [0.85, 0.325, 0.098];

[ax, h1, h2] = plotyy(x, y_1, x, y_2);
set(get(ax(1),'Ylabel'),'String','Data 1', 'Color', 'k');
set(h1,'LineWidth',2,'LineStyle','-','Color',parula_blue,'DisplayName', 'Name 1');
set(ax(1),'ycolor',parula_blue);
set(ax(1), 'YTick', [0 1 2 3 4]);
set(ax(1), 'ylim', [0 4]);

set(get(ax(2),'Ylabel'),'String','Data 2', 'Color', 'k');
set(h2,'LineWidth',2,'LineStyle','--','Color',parula_red,'DisplayName','Name 2');
set(ax(2),'ycolor',parula_red);
set(ax(2),'YDir','reverse');
set(ax(2), 'YTick', [0 0.2 0.4 0.6 0.8 1]);

xlabel('X axis desc')
legend('show')
set(ax, 'XTick', x)

set(ax(1),'Box','off') % Turn off box of axis 1, which removes its right-hand ticks
set(ax(2),'Box','off') % Turn off box of axis 2, which removes its left-hand   ticks

Literator

What about adding hold on plot([0 3],[4-0.001 4-0.001],'k') ? will that do the job for you? – Outwardly

@AnderBiguri: It looks a bit ugly, it doesn't exactly look like the bottom axis line, and it doesn't overdraw the orange/blue ticks at 0/4 the same way. Also it doesn't have the axis-ticks. It would be the last resort solution I guess, but it doesn't look good. – Literator

I agree, it was just worth a try ;) – Outwardly

Out of curiosity (I don't have R2015) what actually happens when you use set(ax(2),'XAxisLocation','top','XTickLabel',[])? Do you get an error message? That's weird this is not working anymore. – Thoracotomy

@Benoit_11: Nothing happens in R2015a. I don't have R2014x anymore but I believe it did the trick on the old version. – Literator

Yes it works perfectly with older versions that's puzzling. – Thoracotomy

Yep, but I think it really does something else anyway: If you try it on ax(1), you'll see it will put the complete axis (including the description) from the top to the bottom, which is not what I want either. I guess it was just "luck" or a bug that it actually did what I wanted it to do with ax(2) on R2014. – Literator

@AnderBiguri is there any reason you subtract 0.001? It looks much nicer if I just use ...,[4 4],.... – Literator

Oh, it looked nicer in my PC, just that. – Outwardly

Answer 1

Based on this answer, you can simply add another axes to your plot, and specify that its horizontal axis is at the top (this code goes at the end of your code):

hBox = axes('xlim', [x(1) x(end)],'XTick', x, 'YTick',[],'XAxisLocation', 'top',...
            'XTickLabel',[]);

Edit:

As per the OP's clarification in the comment, it is possible to draw the black axes "underneath" the blue\orange by reordering the children of the figure, namely, after my above code, add also:

uistack(hBox,'bottom'); %// This sends the black axes to the back.
ax(1).Color = 'none';   %// This makes the plot area transparent for the top axes, so 
                        %// that ticks belonging to the black axes are visible.

---

BTW, I remember using a similar trick when I wanted to have minor and major gridlines with different colors - each set of gridlines belonged to its own axes with their own color.

Anschluss

Your solution draws with black over the blue left y-axis. That's an absolute no-go in this case (you probably didn't notice it I guess). Can you avoid that? – Literator

Also, on the top line, I would like to draw the ticks, but not the labels (0, 1, ...). – Literator

This is some Matlab wizardry. Works perfectly. Thank you very much! – Literator

Answer 2

If you want to avoid adding another set of axes, you can still use ax(2) but you need to make it visible first:

ax(1).Box = 'off';
ax(2).Box = 'off';
ax(2).XAxis.Visible = 'on';
ax(2).XAxisLocation = 'top';
ax(2).XTickLabel = [];
ax(2).XTick = ax(1).XTick ;

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