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Bug 779177 - Regression Equation with Date Axis
Regression Equation with Date Axis
Status: RESOLVED OBSOLETE
Product: libgoffice
Classification: Other
Component: Graphing / Charting
GIT
Other All
: Normal enhancement
: ---
Assigned To: Jean Bréfort
Jody Goldberg
Depends on:
Blocks:
 
 
Reported: 2017-02-24 13:03 UTC by Morten Welinder
Modified: 2018-05-22 13:09 UTC
See Also:
GNOME target: ---
GNOME version: ---


Attachments
Sample file (2.75 KB, application/x-gnumeric)
2017-02-24 13:03 UTC, Morten Welinder
Details

Description Morten Welinder 2017-02-24 13:03:48 UTC
Created attachment 346633 [details]
Sample file

1-Jan-2001	1
1-Jan-2002	3
1-Jan-2003	2
1-Jan-2004	5
1-Jan-2005	4
1-Jan-2006	7
1-Jan-2007	6
1-Jan-2008	9
1-Jan-2009	8
1-Jan-2010	10

Graph that data and add a linear regression and an equation to go with that.
I see "0.00260507x-94.887".

That is, I'm sure, a correct equation, but in contains in it raw information
about the date system we use.

0.002507 makes sense: it is increment per day.

-94.889 does not: it is the predicted Y value for 1-Jan-1900. (Bearing in mind
that we have a hole in the date numbering where 1900-02-29 would have been
and that all date is after that hole, the right date is probably 1899-Dec-31.)

I think we would be better off presenting the result as

   0.00260507(x-"1-Jan-2000")+1.2
Comment 1 Jean Bréfort 2017-02-24 13:14:29 UTC
We clearly need to add a format to the equation (and may be even a format for each coefficient).
Comment 2 Jean Bréfort 2017-02-24 14:38:34 UTC
The other way might be to retrieve the preferred format for the x values, unfortunately, it is not currently possible from the reg curves code. We would need an ABI break, at least (we need a new method in GogSeriesClass).
Comment 3 Morten Welinder 2017-02-24 17:29:34 UTC
It would definitely be useful to have a way to format values used in the
equation.  I don't think it will be very useful to use the X axis format,
though: in y=ax+b, b in units of the Y axis and a is in units of Y/X.
For regressions other than linear regression it is even more complicated.

However, we would need access to the X axis to do the change I mentioned
in the initial report.  We would need to check that

    gog_axis_is_zero_important(axis) == FALSE

before applying the offset-x method.
Comment 4 GNOME Infrastructure Team 2018-05-22 13:09:17 UTC
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This bug has been migrated to GNOME's GitLab instance and has been closed from further activity.

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