ROLLINGKTHLARGEST Function
Computes the rolling kth largest value forward or backward of the current row. Inputs can be Integer, Decimal, or Datetime.
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
and0
, which computes the rolling function from the current row back to the first row of the dataset.
This function works with the Window transform. See Window Transform.
For more information on a nonrolling version of this function, see KTHLARGEST Function.
Wrangle vs. SQL: This function is part of Wrangle, a proprietary data transformation language. Wrangle is not SQL. For more information, see Wrangle Language.
Basic Usage
Column example:
rollingkthlargest(myCol, 2)
Output: Returns the rolling second largest of all values in the myCol
column.
Rows before example:
rollingkthlargest(myNumber, 2, 3)
Output: Returns the rolling second largest value of the current row and the two previous row values in the myNumber
column.
Rows before and after example:
rollingkthlargest(myNumber, 4, 3, 2)
Output: Returns 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
rollingkthlargest(col_ref, rowsBefore_integer, rowsAfter_integer) order: order_col [group: group_col]
Argument  Required?  Data Type  Description 

col_ref  Y  string  Name of column whose values are applied to the function 
k_integer  Y  integer (positive)  The ranking of the value to extract from the source column 
rowsBefore_integer  N  integer  Number of rows before the current one to include in the computation 
rowsAfter_integer  N  integer  Number of rows after the current one to include in the computation 
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. Inputs must be Integer, Decimal, or Datetime values.
Note
If the input is in Datetime type, the output is in unixtime format. You can wrap these outputs in the DATEFORMAT function to output the results in the appropriate Datetime format. See DATEFORMAT Function.
Multiple columns and wildcards are not supported.
Usage Notes:
Required?  Data Type  Example Value 

Yes  String (column reference to Integer or Decimal values)  myColumn 
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.
Note
The value for k
must be an integer between 1 and 1,000 inclusive.
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:
Required?  Data Type  Example Value 

Yes  Integer (positive)  4 
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 value0
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:
Required?  Data Type  Example Value 

No  Integer  4 
Examples
Tip
For additional examples, see Common Tasks.
Example  ROLLINGKTHLARGEST functions
This example describes how to use rolling kthlargest functions for calculating ranking of values within a defined window of rows.
Functions:
Item  Description 

ROLLINGKTHLARGEST Function  Computes the rolling kth largest value forward or backward of the current row. Inputs can be Integer, Decimal, or Datetime. 
ROLLINGKTHLARGESTUNIQUE Function  Computes the rolling unique kth largest value forward or backward of the current row. Inputs can be Integer, Decimal, or Datetime. 
ROWNUMBER Function  Generates a new column containing the row number as sorted by the 
The following dataset contains daily counts of server restarts across three servers over the preceding week. High server restart counts can indicate poor server health. In this example, you are interested in knowing for each server the rolling highest and second highest count of restarts per server over the previous week.
Source:
Date  Server  Restarts 

2/21/18  s01  4 
2/21/18  s02  0 
2/21/18  s03  0 
2/22/18  s01  4 
2/22/18  s02  1 
2/22/18  s03  2 
2/23/18  s01  2 
2/23/18  s02  3 
2/23/18  s03  4 
2/24/18  s01  1 
2/24/18  s02  0 
2/24/18  s03  2 
2/25/18  s01  5 
2/25/18  s02  0 
2/25/18  s03  4 
2/26/18  s01  1 
2/26/18  s02  2 
2/26/18  s03  1 
2/27/18  s01  1 
2/27/18  s02  2 
2/27/18  s03  2 
Transformation:
First, you want to maintain the row information as a separate column. Since data is ordered already by the Date
column, you can use the following:
Transformation Name 


Parameter: Formula type  Single row formula 
Parameter: Formula  ROWNUMBER() 
Parameter: New column name  'entryId' 
Use the following function to compute the rolling kth largest value of server restarts per server over the previous week. In this case, you can use the ROLLINGKTHLARGEST
function, setting k=1. Uniqueness doesn't matter for calculating the highest value:
Transformation Name 


Parameter: Formula type  Multiple row formula 
Parameter: Formula  rollingkthlargest(Restarts, 1, 6, 0) 
Parameter: Sort Rows by  Server 
Parameter: Group Rows by  Server 
Parameter: New column name  'rollingkthlargest_1' 
Use the following function to compute the rolling second highest value. In this case, you can use ROLLINGKTHLARGESTUNIQUE
:
Transformation Name 


Parameter: Formula type  Multiple row formula 
Parameter: Formula  rollingkthlargestunique(Restarts, 2, 6, 0) 
Parameter: Sort Rows by  Server 
Parameter: Group Rows by  Server 
Parameter: New column name  'rollingKthLargestUnique_2' 
Results:
entryId  Date  Server  Restarts  rollingKthLargestUnique_2  rollingkthlargest_Restarts 

3  2/21/18  s02  0  0  0 
6  2/22/18  s02  1  0  1 
9  2/23/18  s02  3  1  3 
12  2/24/18  s02  0  1  3 
15  2/25/18  s02  0  1  3 
18  2/26/18  s02  2  2  3 
21  2/27/18  s02  2  2  3 
4  2/21/18  s03  0  0  0 
7  2/22/18  s03  2  0  2 
10  2/23/18  s03  4  2  4 
13  2/24/18  s03  2  2  4 
16  2/25/18  s03  4  2  4 
19  2/26/18  s03  1  2  4 
22  2/27/18  s03  2  2  4 
2  2/21/18  s01  4  4  4 
5  2/22/18  s01  4  4  4 
8  2/23/18  s01  2  2  4 
11  2/24/18  s01  1  2  4 
14  2/25/18  s01  5  4  5 
17  2/26/18  s01  1  4  5 
20  2/27/18  s01  1  4  5 