For purposes of this calculation, two instances of the same value are treated at one value for k. So, if your dataset contains four rows with column values 10, 9, 9, and 8, then KTHLARGESTUNIQUE returns 9 for k=2 and 8 for k=3.

ROLLINGKTHLARGESTUNIQUE computes the KTHLARGESTUNIQUE value across a defined window of values within a column.

• If an input value is missing or null, it is not factored in the computation. For example, for the first row in the dataset, the rolling calculation of previous values is undefined.

• The row from which to extract a value is determined by the order in which the rows are organized based on the order parameter. 

  If you are working on a randomly generated sample of your dataset, the values that you see for this function might not correspond to the values that are generated on the full dataset during job execution.

• Inputs:
  • Required column name
  • Required kth value, which is a positive integer 
  • Two optional integer parameters that determine the window backward and forward of the current row. The default integer parameter values are -1 and 0, which computes the rolling function from the current row back to the first row of the dataset.
• This function works with the following transforms:
  • Window Transform
  • Set Transform
  • Derive Transform

For more information on a non-rolling version of this function, see KTHLARGESTUNIQUE Function.

Column example:

Output: Generates a new column containing the rolling second largest unique value in the myCol column from the first row of the dataset to the current one.

Rows before example:

Output: Generates the new column, which contains the rolling second largest unique value of the current row and the two previous row values in the myNumber column.

Rows before and after example:

Output: Generates the new column, which contains the rolling fourth largest unique value of the two previous row values, the current row value, and the two rows after the current one in the myNumber column.     

For more information on the order and group parameters, see Window Transform.

col_ref

Name of the column whose values are used to compute the function. 

• Multiple columns and wildcards are not supported.

k_integer

Integer representing the ranking of the unique value to extract from the source column. Duplicate values are treated as a single value for purposes of this function's calculation.

• k=1 represents the maximum value in the column. 
• If k is greater than or equal to the number of values in the column, the minimum value is returned.
• Missing and null values are not factored into the ranking of k.

rowsBefore_integer, rowsAfter_integer

Integers representing the number of rows before or after the current one from which to compute the rolling function, including the current row. For example, if the first value is 5, the current row and the four rows after it are used in the computation. Negative values for rowsAfter_integer compute the rolling function from rows preceding the current one.

• rowBefore=1 generates the current row value only.
• rowBefore=-1  uses all rows preceding the current one.
• If rowsAfter is not specified, then the value 0 is applied.
• If a group parameter is applied, then these parameter values should be no more than the maximum number of rows in the groups.

Example - ROLLINGKTHLARGEST functions