• 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 count of non-null values 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.

• The function takes a column name and 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 Window transform. See Window Transform.

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

Column example:

Output: Returns rolling count of non-null values in the myCol column.

Rows before example:

Output: Returns the rolling count of non-null values of the current row and the three previous row values in the myNumber column.

Rows before and after example:

Output: Returns the rolling count of non-nulls from the three 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.

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 five rows before it are used in the computation. Negative values for rowsAfter_integer compute the rolling function from rows preceding the current one.

• rowBefore=0 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 - Counting messages

In the following example, messages are tabulated every 10 seconds from a system. If no message is generated, null values are returned. 

Source:

Transformation:

You are interested in counting the number of entries for the preceding minute for each row. You add the following:

Results: