How to set text position in yyaxis?

Hi all

I tried to set text position as following. It was OK.

t = 1:0.1:10;
yyaxis('left');
plot(t, sin(t), 'b.-', 'LineWidth', 2);
ylabel('sin');
hold on
yyaxis('right');
plot(t, cos(t)*2, 'g.-', 'LineWidth', 2);
ylabel('cos');
xlabel('Time[ms]');
grid on;

yyaxis('left');
text(4, 0.5,'left=0.5') %I would like this to be referenced to the 2nd y-axis

yyaxis('right');
text(4, 0.5,'right=0.5') %I would like this to be referenced to the 1st y-axis

hold off

But now I want to change text by set

t = 1:0.1:10;
yyaxis('left');
plot(t, sin(t), 'b.-', 'LineWidth', 2);

ylabel('sin');
hold on
yyaxis('right');
plot(t, cos(t)*2, 'g.-', 'LineWidth', 2);
ylabel('cos');
xlabel('Time[ms]');
grid on;

hText = nan(1, 2);
for cnt = 1:2
    hText(cnt) = text(NaN, NaN, '', ...
                  'BackgroundColor', 'yellow');
end

yyaxis('left');
set(hText, 'Position', [4, 0.5], 'String', 'left=0.5');
%text(4, 0.5,'left=0.5') %I would like this to be referenced to the 2nd y-axis

yyaxis('right');
set(hText, 'Position', [4, 0.5], 'String', 'right=0.5');
%text(4, 0.5,'right=0.5') %I would like this to be referenced to the 1st y-axis

hold off

you can see that, can't display [left=0.5] following 1st y-axis.

Do anyone know why? Please explain and tell me how to fix.

thank you

Answer 1

[dpb]

t = 1:0.1:10;
yyaxis('left');
plot(t, sin(t), 'b.-', 'LineWidth', 2);
ylabel('sin');
text(4,0.5,'left=0.5','BackgroundColor','y');

yyaxis('right');
plot(t, cos(t)*2, 'g.-', 'LineWidth', 2);
ylabel('cos');
xlabel('Time[ms]');
text(4,0.5,'right=0.5','BackgroundColor','y');
yl=ylim;yticks(linspace(yl(1),yl(2),11))        % make grids align both axes
grid on;

Do what needs doing on each axis when there to begin with.

While what you had will work; it's a lot more trouble switching back and forth than finishing the job when there.

The specific problem in your code is the two lines

...
set(hText, 'Position', [4, 0.5], 'String', 'left=0.5');
...
set(hText, 'Position', [4, 0.5], 'String', 'right=0.5');
...

hText is the array of BOTH handles; each call sets the position of both in turn to the same place on the axis presently in focus. So, the last axis to have focus and the call wins.

BTW when allocating space for future graphics objects, instead of

hText = nan(1, 2);

use

hText = gobjects(1, 2);

which is expressly for the purpose.

[galaxy]

@dpb

So you mean that can not use set function, right?

set(hText, 'Position', [4, 0.5], 'String', 'left=0.5');

[dpb]

Well, you can use set(), but not for both handles at the same time, no, and address the two axes independently.

One and only one axis will be the current axes at the time the call is made and whichever is the last to be "it" wins...

Why would you want to; the code I showed that does as wanted is one(!) whole line more in what it does and actually removes four lines of an unneeded for...end loop so is, overall less code to write.

The point is, you have to address each axis while it is gca or use the axis handle in the function call to put the object on the axis desired. That was doable with the old plotyy that returned the two axes handles, but yyaxis does NOT return axes handles; one can only swap back and forth by calling yyaxis with the keyword 'left' or 'right'; there's no alternative way to address the other axis than the current one without the intermediate step of swapping.

Why are you so adamant about using set here, pray tell???

[galaxy]

@dpb

I need to use function and call other function.

So, I can not use yyaxis('left'); yyaxis('right'); anytime.

But, I think that can use set() at same time by initialize first.

anw, thank you your anwser. This topic will close in here.

[dpb]

What you think and what happens have been demonstrated to not be consonant in results desired...