Sliding Calculation

The 'Sliding' calculation allows you to express each group's value as an accumulation of neighboring aggregate values in the series, specified by a rectangular sliding window. This generally has the effect of smoothing (low-pass filtering) the displayed data.

 

The method of accumulation is specified by the 'Aggregate' menu in the 'Calculation' dialog box. (See Aggregation Options for more information about the different methods.) The 'Previous' and 'Next' values specify the span of the sliding window as the number of preceding and succeeding groups, respectively, to include in the calculation. All included groups have equal weight in the calculation.

The 'Include current value' options incorporates each group's aggregate value into its own calculation. When this option is not enabled, the calculation for a group uses only its neighboring groups' values. For example, assume the chart displays sales totals for March, April, May, June, and July, and the sliding window is 3 units wide ('Previous'=1 and 'Next' =1). If 'Include current value' is enabled, the displayed value for May is aggregated from three months' data, April, May, and June. However, if 'Include current value' is not enabled, the displayed value for May is aggregated from two months' data, April and June.

The 'Null if not enough values' option suppresses chart points for which the sliding window does not obtain the required span. For example, assume the chart displays sales totals for March, April, May, June, July, August, and September, and that the sliding window is 5 units wide ('Previous'=2 and 'Next' =2). If 'Null if not enough values' is enabled, then no points are displayed on the chart for the months of March and April because the calculation cannot be performed for these groups as specified (there is no data available preceding March.) However, if 'Include current value' is not enabled, the aggregates for March and April will be computed and displayed using the data available within the sliding window.

See Also

Running Calculation, to accumulate values from the start of the series.

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