GNOME Bugzilla – Bug 605041
Regression lines need labeling features
Last modified: 2018-05-22 13:04:20 UTC
Regression lines need a number of other features to make them really useful: (1) When adding a regression line to a graph, it is often really important to display the "r value" (Pearson's correlation coefficient, given by =correl() ) right next to the regression line. This should be manually moveable in case the automatically-assigned location is undesirable. (2) The actual equation of the regression line (whether linear or otherwise) needs to be able to be added (and possibly repositioned) too. (3) It would be immensely helpful if "axis intercept lines" could be added to any regression line: given a certain X value, calculate the corresponding Y value of the regression line for that X value, and then draw a vertical line from the X axis up to the regression line, and then a horizontal line from the regression line to the Y axis. These lines could optionally extend the entire width and height of the graph, or just the partial distance from the axis to the regression line. This allows for certain points of interest (e.g. thresholds) to be clearly shown on the graph.
(1) and (2) are already implemented (since a long time, btw). Just the equation and R-squared can't be positioned independently. Do I miss something? (3) If I understand correctly, you want to be able to add drop-lines to the regression curve. This seems quite possible to implement, but needs some work, so probably after 1.10.
Ah, on (1) and (2), I didn't realize after adding a regression line you can add the equation to the regression line. However this exposes a few more issues: Replace (1), (2) with (4): Yes, the box needs to be able to be manually positioned. (5) If you have two series each with their own trendlines, (or presumably two trendlines on one series), their boxes overlap and you can only see the equation for one series. They need to be staggered when being added, if they have not been manually positioned. (And if trendlines are added/removed, they need to be re-staggered.) (6) The user should have the option of displaying R and not just R^2. yes, (3) is about adding drop-lines to the regression curve for specific values of X and/or Y. (You should be able to choose which of X or Y is fixed, then the other value should be calculated/re-calculated when the regression line is changed, and droplines should be shown to both axes.) I'll attach a chart showing the concept, where the droplines for both regression lines are derived from an X-value of 106.
Created attachment 150098 [details] Chart showing two examples of (3), one for each regression line, based on an X value of 106. (Ignore the extra text written over the chart, it is not relevant.)
The box can be manually positioned. Just try.
You are right, I can manually position the box -- but only if I select it in the treeview and then drag it, not if I try to select it or drag it in the preview in chart properties (that just drags the whole chart). I guess it seems like that's how everything else works in chart properties though. (Initial staggering would still be important in the case of multiple equations, to prevent overlap.)
You can select it in the preview and drag it. I agree that staggering would be nice. We might also limit the displayed segment, there are so many possible enhancements...
*** Bug 433936 has been marked as a duplicate of this bug. ***
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