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Could not complete Forecast in line chart with error "Forecast - Holt-Winters calculations require the data points to be spaced at equal distances."

Rich Talbot
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Product: TIBCO Spotfire®

Problem:

Could not complete Forecast in line chart with error "Forecast - Holt-Winters calculations require the data points to be spaced at equal distances."


Solution:

When you add or edit a Holt-Winters forecast from the Lines & Curves page of the Visualization Properties dialog (only available for some visualization types), or by right clicking and enabling Forecast, the following error message is seen, "i" informational alert next to viz title: 

Forecast - Holt-Winters calculations require the data points to be spaced at equal distances.

If you show markers, you see that the x-axis has all months and there is not data for all months. This is caused by setting x-axis mode as "Show filtered range", while there are missing values for some of the months. Go to:
  • Properties > X-axis > Columns: Settings > Axis Mode: Categorical > Categories. Change that from "Show filtered range" to "Show filtered values".
Or alternatively:
  • Properties > Appearance > Time Series: Check "Compensate for missing values" . You may need to change the y-axis to something like Count([AnyColumn]). This option allows you to have all 12 months of every year on the x-axis, if that is what is desired.
Doc: Curve Fit Models > Holt-Winters Forecast

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