Use this dialog to create a preceding value calculation. A preceding value calculation returns the value that is a specified number of rows or a specified time period before each value. For example, you might want to know what the previous month's sales are for each value.
You typically create preceding calculations for use in other calculations. For example, you might use the preceding month's sales values to calculate the change in sales from the previous month.
This type of analysis is sometimes referred to as LAG/LEAD analysis.
Note: To return a following value rather than a preceding value, use the Following Value dialog (see "Following Value dialog").
For more information, see:
"What are analytic functions?"
"Examples of using row-based and time-based intervals"
"How to create a calculation using an analytic function template"
Use this drop down list to choose the item for which you want to return the preceding value. For example, you might choose Sales SUM to calculate a previous sales value.
Use this drop down list to specify the number of rows or the number of time periods in which you want to compare the values. For example, you might choose '3' to compare sales values with earlier sales values.
Use the adjacent drop down list to choose a row-based interval or a time-based interval. For example, you might choose Months Preceding Current Value to compare sales values with earlier sales values.
Hint: If you have time-based data, use time-based groups (for example, Days/Weeks/Months Before Current Value). If you do not have time-based data, use row-based groups (for example, Rows Before Current Value). For more information about types of group, see "About windowing".
For examples of specifying row-based and time-based intervals, see "Examples of using row-based and time-based intervals".
Use this drop down list to specify how to order the worksheet values. For example, you might choose Calendar Month to compare sales with the previous month's sales.
Use the adjacent drop down list to specify whether to order values in ascending order (that is, Lowest to Highest) or descending order (that is, Highest to Lowest).
Hint: If you have specified a time-based group in the Return value fields, specify a time-based value in the Order rows by fields (for example, Calendar Month).
Use this drop down list to specify a secondary order for the values. For example, you might choose 'City' to sort values on city within month.
Use the adjacent drop down list to specify whether to order values in ascending order (that is, Lowest to Highest) or descending order (that is, Highest to Lowest).
Restart calculation at each change in
Use this list to specify the groups to be used to arrange results into groups (sometimes referred to as partitions).
For example, to calculate the preceding value of sales values of months within each year, you might choose Calendar Year.
If you do not specify a group, Discoverer treats all worksheet values as a single group.
This read-only field displays the underlying formula that you are building as you specify values for the fields above. This formula is updated each time you change one of the values in the fields above. When you click OK, the formula is transferred to the Calculation field in the "New Calculation dialog" or the "Edit Calculation dialog".
A preceding value calculation returns a null value if there is no preceding value.