More Than Just a Check-Box

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Friday, 12 Oct 2007

More Than Just a Check-Box

Bjoern Milcke

Issue 7998 is quite old, as you can see by the low number. It was submitted half a decade ago. It's issue: equations for trend-lines. This is one of the issues that haven't been done for quite a long time due to the re-implementation of the chart. Now, that we have the new chart in OpenOffice.org 2.3, I took care of it and finished almost by now. The UI is still not optimal. As we have a nice code-base now, the implementation was for sure much more fun than it would have been for the old implementation, but it was far more than a check-box (that's what was stated at one point in the comments of issue 7998) — I can tell you that much!

Example Chart with Regression Equations
This is an example using the new feature. I chose only linear regressions in this example, but of course this feature works for all supported regression types. I was looking for some data that can nicely be used for regression curves, and found some here. And only after I created the chart I noticed that the new feature is really useful, you can see:

R² is very small, i.e. the linear regression is not a very good match, or in other words the variance of the data is quite large.
Ignoring the first fact you could interpret the equation and find out that the temperature rose about two percent over the years. It's up to you to conclude global warming out of this data, though.

So, whenever chart17 is integrated, this feature will make it into OpenOffice.org.

What you can do now is, insert an equation for each regression curve (that's how trend-lines are still called in OOo). You can display the equation itself, the square of the correlation coefficient R, or both together. The text can be formatted with borders, a fill style and different fonts and font effects. The number format for all numbers appearing in the formula or in R² can be set. The equations are initially placed on the left and aligned with the top of the bounding box of the curve, which is not the most sophisticated place, but you will usually move the formula around anyway to have it at a place where it is well visible.

The necessary file format extensions for this feature have been integrated into the ODF 1.2 draft by the OASIS OpenDocument TC.

P.S.: For those who are wondering about the smooth rendering: this is a screen shot of an exported PDF.

tags: chart openoffice.org

Posted by Bjoern Milcke on 12 Oct 2007 | PermaLink |

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Comments

Joseph said:

AWESOME. Been hoping for this for quite a while. Hope it lands soon and gets out into the wild.

Posted by Joseph on October 12, 2007 at 05:21 PM CEST #

Cancel said:

Oh I simply love it. It's functional. It's what is needed in the wild. Where is the button to vote for "chart17-devs" for president? This and the missing error bars (can you also comment on this?) are the two major issues to me. It's hard to work in R&D without having this handy. My workaround so far was gnumeric (or EXCEL-Viewer + screenshot). This will soon be something of the past.

Posted by Cancel on October 12, 2007 at 05:47 PM CEST #

Pete said:

One thing I forgot. To look for some real data sets take a look at the R-project (www.r-project.org). There are certainly plenty of data (also some at the edge) useful for you purposes. Moroever you can compare your results with that of a scientific (thus somewhat proven) tool.

Posted by Pete on October 12, 2007 at 05:52 PM CEST #

Jeff said:

When will this be implemented within OO.....I am using v2.3.

Posted by Jeff on November 05, 2007 at 06:41 PM CET #