
1. Re: Trend line slope (and pvalue)
Michael Cristiani Aug 19, 2010 8:18 PM (in response to . Andrew26)Andrew,
Do you want to do this automagically or one trend line at a time interactively? There are some ways to do this kind of thing, but the route depends on how the visualizations will be consumed or used. Can you provide a bit more information?
MANY BLESSINGS!
Peace and All Good!

2. Re: Trend line slope (and pvalue)
. Andrew26 Aug 20, 2010 11:16 AM (in response to . Andrew26)Thanks for replying, mcristia.
The trendline slopes I'd like to see are those of about 55 different customers which are shown on one line graph (I know that's a lot for one graph, but I have it set up so they're highlighted when I click in the adjacent table)
I know I can hover over the trendline and it shows the slope, and I know you can describe the trend model by right clicking on the chart. However, this is not useful to me.
What I want is to have a calculated field that presents the all 55 trendline slopes as numbers next to in a table.
Possible?

3. Re: Trend line slope (and pvalue)
Brandon Smith May 28, 2011 10:30 AM (in response to . Andrew26)I wanted to bump this as well because I have a similar scenario. I am trying to create an optimal pricing model so if I use the base trend line it's no good because my customers with poor margins bring down the trend. I would like to be able to adjust and calculate a line and plug in that formula and at the minimum have Tableau draw it for me (at maximum be able to use it in calculated fields). Right now I am having to export it out as an image and using a photo editor to draw the line.

4. Re: Trend line slope (and pvalue)
Joe Mako May 28, 2011 5:17 PM (in response to . Andrew26)Brandon,
With custom table calculations, I believe what you are looking can be done, but you would need to provide sample data, and the formulas and/or business logic you want applied, and what you expect for a result. With additional details and specifics on what you have and what you are looking for, assistance can be provided.

5. Re: Trend line slope (and pvalue)
petermayer May 29, 2011 12:10 PM (in response to . Andrew26)Hi there,
I want to bump this thread  did any of you find a solution?
What I want to do is to "fetch" the last value of a trendline and use it in a calculated field.
As far as I can tell I would somehow calculate the field myself, if I know how the trendline is calculated, right?
So if I use "Describe the Trend Model" I get the "Model Formula" which I do not understand. It multiplies some values and then adds an intercept.
Is there a way to logically derive the necessary structure of a calculated field from a trend line? Where would I start?
Thanks,
Peter

6. Re: Trend line slope (and pvalue)
petermayer Jun 1, 2011 1:39 PM (in response to . Andrew26)Any news on this one? :)

7. Re: Trend line slope (and pvalue)
petermayer Jun 4, 2011 8:50 AM (in response to . Andrew26)So I reckon no?
Would it help to contact customer support?

8. Re: Trend line slope (and pvalue)
Joe Mako Jun 4, 2011 9:21 AM (in response to . Andrew26)Peter,
does: http://www.alansmitheepresents.org/2011/06/fittedcurvemodelingintableau.html help your situation?
or are you looking for something like: The specified item was not found.
or do any of the comments at http://www.tableausoftware.com/support/forum/topic/forecastinghow address your situation?
If these do not help your situation, then if you can provide a sample packaged workbook that represents your situation and detail what you expect for a result, an example solution can be made.

9. Re: Trend line slope (and pvalue)
Philip George Aug 10, 2012 3:04 AM (in response to Joe Mako)Hi,
I saw one feature which helps for advanced analysis in the below link.
http://community.tableau.com/message/181143#181143
I think this feature can help us for doing prediction also.Am I correct?
Philip

10. Re: Trend line slope (and pvalue)
Andrew Hill Nov 1, 2012 2:39 PM (in response to . Andrew26)Greetings,
There seems to be a lot of interest in being able to calculate the slope for a linear regression in Tableau above and beyond the built in trend line. This makes sense as sometimes you might want to sort or isolate things with certain slopes. I would give this calculation a shot:
(size()*window_sum(sum([x])*sum([y]))window_sum(sum([x]))*window_sum(sum([y])))
/
(size()*window_sum(power(sum([x]),2))power(window_sum(sum([x])),2))
Here your [x] field is your x axis and your [y] field is your y axis.
For time series it might be a little more difficult. If you have data by day, I might try making your [x] field something like: datediff('day',today(),[Date]) assuming you don't have data going out into the future. If you do, you can just anchor the datediff calc to a random date in the past before your data starts (datediff('day',date(1/1/1998),[Date])).
EDIT: or you can just be smart and create a field float([Date]) and use that instead
This should pull out your slope value. You can back into your intercept and rsquared with similar logic.
Remember that this is a table calculation so if you are looking to slice this up by a dimension will most likely need to edit your table calc to restart every [dimension] (and change the compute using).

11. Re: Trend line slope (and pvalue)
Joey Minix Apr 27, 2015 12:08 PM (in response to Andrew Hill)2 of 2 people found this helpfulAnyone finding this by searching and wants to see how to calculate slope of a trendline using LOD expressions:
I'm mimicking this formula to obtain slope: y = αx + β
where α = (n∑(xy) ∑x ∑y) / (n∑x^2 (∑x)^2 )
({fixed:count([X])}*{fixed:sum([Y]*[X])}  {fixed:sum([X])}*{fixed:sum([Y])}) /
({fixed:count([X])}*{fixed:sum(power([X],2))}power({fixed:sum([X])},2))
Where [X] is your xaxis, [Y] is your yaxis
If your xaxis is a date, create a calculated field of float([X]) called floatdate. Substitute [X] in the formula with your new calculated field, like so:
({fixed:count([X])}*{fixed:sum([Y]*[floatdate])}  {fixed:sum([floatdate])}*{fixed:sum([Y])}) /
({fixed:count([X])}*{fixed:sum(power([floatdate],2))}power({fixed:sum([floatdate])},2))
Obviously, if you need to edit the level of detail, add the necessary fields between 'fixed' and the colon.

12. Re: Trend line slope (and pvalue)
Kris Erickson Oct 28, 2015 3:10 PM (in response to Joey Minix)Joey, This method worked splendidly. Thank you for your contribution to the community.
The only thing is that I think it does not handle situations where my LOD has NULLs, but that's on my end.

13. Re: Trend line slope (and pvalue)
Michael Monoski Jun 16, 2016 9:24 AM (in response to Joey Minix)Joey,
I have a very similar case, but can't seem to get the formula to provide the right answer.
I'm attaching a sample .twbx
For the data that's in there, Tableau is calculating a slope of .224237 when I bring in a linear trend line. I want to create a calculated field that will return that same result, but I have been unable to get the same result using your guidance above. I think it might be related to fact that my Y value is already an AGG function. If you could take a look, I would really appreciate it. Let me know if you have any questions.
Y should be Unit Price
X should be Year
*I have multiple records in a given year, so that's why my unit price is already a AGG function: sum([Net value])/SUM([Order Quantity])

Sample Workbook.twbx 16.2 KB


14. Re: Trend line slope (and pvalue)
Luke Bullard Sep 23, 2019 7:47 PM (in response to Joey Minix)Here's a template based on Joey's that lets you run an IF statement on each row to determine if it should be included. Just replace <EXPRESSION> with your expression. If you can throw your dimension in the LOD expression instead of the IF statement, do that as a first option.
(
{FIXED : COUNT(IIF(<EXPRESSION>,[X],NULL))} * {FIXED : SUM(IIF(<EXPRESSION>,[Y] * [X],NULL))}
 {FIXED : SUM(IIF(<EXPRESSION>,[X],NULL))} * {FIXED : SUM(IIF(<EXPRESSION>,[Y],NULL))}
) /
(
{FIXED : COUNT(IIF(<EXPRESSION>,[X],NULL))}
* {FIXED : SUM(IIF(<EXPRESSION>,POWER([X], 2),NULL))}
 POWER({FIXED : SUM(IIF(<EXPRESSION>,[X],NULL))},2)
)