What is the Best Way to Deal with an Empty Line Object?
13 views (last 30 days)
Show older comments
Suppose I have some data:
x = 1:10; y = 1:10;
Now I want to plot three lines based on three logical index vectors.
i1 = x<=3;
i2 = x > 3 & x < 7;
i3 = x >= 7;
hlines = plot(x(i1),y(i1),'r',x(i2),y(i2),'b',x(i3),y(i3),'g');
legend(hlines,'first','second','third');
So far so good. Now suppose i2 is empty
i1 = x<=3;
i2 = x > 100;
i3 = x >= 7;
hlines = plot(x(i1),y(i1),'r',x(i2),y(i2),'b',x(i3),y(i3),'g');
legend(hlines,'first','second','third');
Oops, the legend is not what I want; green should be 'third'.
One way to deal with this is to append NaN to all inputs
hlines = plot([x(i1) nan],[y(i1) nan],'r',[x(i2) nan],[y(i2) nan],'b',[x(i3) nan],[y(i3) nan],'g');
legend(hlines,'first','second','third');
I don't mind that 'second' shows up in legend, even though there is no line. In fact, that's preferred. Keep in mind that all this is in a function and there is no way to know a priori of any of i1, i2, i3 will be empty.
Is there a better way to make sure the the legend is consistent regardless of whether or not i1, i2, or i3 is empty?
0 Comments
Accepted Answer
Walter Roberson
on 13 Jun 2021
i1 = x<=3;
i2 = x > 100;
i3 = x >= 7;
plot(x(i1),y(i1),'r',x(i2),y(i2),'b',x(i3),y(i3),'g');
hold on
hlines = plot(nan,nan,'r', nan, nan, 'b', nan, nan, 'g');
legend(hlines, {'first', 'second', 'third'});
That is, when your legend does not necessarily match the graphic objects exactly, then create fake invisible graphic objects and legend() those.
This technique is very useful for situations such as scatter() where the number of graphics objects being created does not match the number of classes needed to be described.
5 Comments
Walter Roberson
on 13 Jun 2021
Some of the issues can be reduced by setting Tag for the objects and the same Tag for the proxy line being used for the legend.
obj1 = findobj(ax, 'Tag', 'first');
set(obj1, 'color', 'k', 'Marker', '*')
More Answers (1)
Steven Lord
on 13 Jun 2021
x = 1:10;
y = 1:10;
i1 = x<=3;
i2 = x > 100;
i3 = x >= 7;
hold on
plot(x(i1),y(i1),'r','DisplayName', 'first');
plot(x(i2),y(i2),'b','DisplayName', 'second');
plot(x(i3),y(i3),'g','DisplayName', 'third');
legend show
1 Comment
Walter Roberson
on 13 Jun 2021
This does help, but the user prefers that second also show up, even if there are no visible lines for it.
See Also
Categories
Find more on Specifying Target for Graphics Output in Help Center and File Exchange
Community Treasure Hunt
Find the treasures in MATLAB Central and discover how the community can help you!
Start Hunting!