Previous Value Analytic Function

This article describes how to use the Previous Value analytic function in CDP Data Visualization.

  1. Click the field on the measurement shelf, in this case, the sum(population) field on the Y Axis shelf.
  2. In the Field Properties menu, expand Analytic Functions, and select Previous Value.
  3. In the Analytic Function: Previous Value modal window,
    1. In Select aggregate for this measure, leave the default Sum. The other aggregation options are Count, Minimum, Maximum, and Average. In addition, some connection types also support Approximate Distinct Count and Exact Distinct Count.
    2. Under Select entities over which to tale previous value, select state. This is the grouping that applies when calculating previous values.
    3. Under Select the sort order, click the Plus icon, select year, and then set it to ascending sort order. This order specifies what determines what the previous row is, and the row where the value is taken.

      Note that you can add additional sort parameters, by clicking the Plus icon.

    4. Under Offset, specify the number of previous rows over which the function executes.

  4. Click Apply.
  5. Optional: If you examine the expression in the Enter/Edit Expression interface, it shows that the function has the following form: LAG(sum([population]), 1) over (partition by [year] order by [year], [country]) as 'previous value(population)'
  6. Click Refresh Visual.
  7. Notice the change to the appearance of the visual, and the change in values that appear on the tooltip.