Spotfire调试经验——移动平均值的动态计算（Dynamic calculation of moving average in Spotfire visualization）

各季度销售额的折线图如下所示：

问题：如何展现出过去时间段内（年、季度、月、星期、天、小时、分、秒）的移动平均值？

解决方案：单击图标左侧Y轴销售额，编辑公式为“Sum([Sales Total]) OVER (LastPeriods(3,[Axis.X]))/ 3”，即可实现该要求。其中的3表示过去3期（包括当期，用户可自己指定）

---------------------------------------------------------------------------------------------------------------

以下内容摘自官网文档：

The OVER functions are used to determine how data should be sliced, for example, relative to time periods. For more information, see OVER in Custom Expressions and Advanced Custom Expressions.

Option: AllPrevious()

Uses all nodes, includingthe current, from the start of the level. This can be used to calculate thecumulative sum.

Examples:

Sum([Sales]) OVER(AllPrevious([Axis.X]))

Sum([Sales]) OVER(Intersect(Parent([Axis.X]), AllPrevious([Axis.X])))

以下内容摘自培训资料：

The LastPeriods() method will look for "back" as many nodes as you ask for.  This function asks for an input value to determine that number.

A great example of a way to use this method is to calculate moving averages.