ROLLINGKTHLARGEST Function

KTHLARGEST extracts the ranked value from the values in a column, where k=1 returns the maximum value. The value for k must be between 1 and 1000, inclusive. For purposes of this calculation, two instances of the same value are treated as separate values. So, if your dataset contains three rows with column values 10, 9, and 9, then KTHLARGEST returns 9 for k=2 and k=3.

ROLLINGKTHLARGEST computes the KTHLARGEST 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 KTHLARGEST Function.

Basic Usage

Column example:

derive type:single value:ROLLINGKTHLARGEST(myCol, 2)

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

Rows before example:

window value:ROLLINGKTHLARGEST(myNumber, 2, 3)

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

Rows before and after example:

window value:value:ROLLINGKTHLARGEST(myNumber, 4, 3, 2)

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

Syntax and Arguments

window value:value:ROLLINGKTHLARGEST(col_ref, rowsBefore_integer, rowsAfter_integer) order: order_col [group: group_col]

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

For more information on syntax standards, see Language Documentation Syntax Notes.

col_ref

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

• Multiple columns and wildcards are not supported.

Usage Notes:

k_integer

Integer representing the ranking of the unique value to extract from the source column. Duplicate values are treated as separate values 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.

Usage Notes:

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 k compute the rolling average 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.

Usage Notes:

Examples

Example - ROLLINGKTHLARGEST functions