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Yes I am.
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You're not going to be able to use Tableau's built-in forecasting with the view or data that you've provided, for a three reasons:
1) There's not enough detail in the data for Tableau to compute a forecast, I'm not sure of the minimum number of date increments but it's definitely more than 4.
2) When a view includes table calculations (which yours does), Tableau won't compute a forecast.
3) We don't have access to the forecasted to either dynamically set a number of them nor to append another measure just to the forecasted results.
Therefore, you're going to have to define your own forecasting algorithm and set up the data to take advantage of that. Based on what you'd posted, I'd add a column to the data that has the max reporting date (if you have multiple subgroupings/aggregations of the data, then you might need multiple columns for different aggregation levels), and add a "Source" column to identify the original data, then add a row to the data for every distinct grouping that you'll be filtering for (in your sample data you'd need two rows, one for each ORFAC). This data will have the max date for the data, and a value for "padding" in the padding column. This can be a static view in Excel, or something built more dynamically either through formulae in Excel or Custom SQL.
Then you can create a calculated field for the "Period for Forecast" that is something like
WHEN 1 THEN [Period] //raw data
WHEN 2 THEN DATEADD('year',[Expiration Extended (Years)]-1,DATEADD('year',[Max Period]-2000,#1/1/2000#)) //padded data
Once you bring that into a view, turn on Show Missing Values for that date pill and Tableau will automatically pad out the dates between the Max Date and your extended date. Note that the DATEADD('year'... only takes integers, and you'd set up a decimal Expiration Extended parameter, so that calc may need to be modified if you want to extend by fractions of years.
Then your forecasting algorithm and calc for adding capital can be built using table calcs. If you need help with that, feel free to post again here and I'll check it out.
Your explanation is clear, but I don’t think that I completely understand how to change the source data according to your suggestion. If you have a moment would you mind showing me what you mean.
Testing Trend Visual.xlsx 40.0 KB