How to add a 1:1 reference line

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Ellen Maas
Ellen Maas on 13 Nov 2020
Commented: Star Strider on 14 Nov 2020
Hi, I am trying to add a dashed 1:1 reference line to subplots of data correlations. The range of values is the same for both x and y.
I have tried refline, but it appears to be tied to the range of the data, such that it only extends across the plot where there are data points.
For example:
In the plot above, the 1:1 line stops short of the lower-left and upper-right corners. I want a line that goes all the way from the point of origin to the upper right-hand corner of the plot, such as in this plot:
It only works in this graph because there are data points closer to the corners. I want a line that is not dependent on the data, like xline or yline, but has a slope of 1.
Any help is greatly appreciated!

Accepted Answer

Star Strider
Star Strider on 14 Nov 2020
I am not certain what you want.
Try this:
x = rand(1,10); % Create Data
y = rand(1,10); % Create Data
figure
plot(x, y, '.')
hold on
plot(xlim, ylim, '--r')
hold off
legend('Data', 'Reference Line', 'Location','SE')
.
  5 Comments
Ellen Maas
Ellen Maas on 14 Nov 2020
So I just tried this, and it works for all the graphs and axis ranges:
plot([0 ylim*2], [0 ylim*2], '--r')
Now the line extends all the way across. None of my axes are less than 0, so having 0 as the minimum value will not cause any problems.
Thank you for your help in thinking this through!
Star Strider
Star Strider on 14 Nov 2020
As always, my pleasure!
If any are less than 0, an extension of this idea will work similarly:
plot([min([xlim ylim]) max([xlim ylim])], [min([xlim ylim]) max([xlim ylim])], '--r')
That generalises it to any range.

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