Window Loop Start

The Window Loop Start node takes a table as input and defines a window of a certain size. In each iteration a chunk of rows of the input table is returned and the window is moved by a defined step size until the end of the table is reached. The returned chunks contain rows, which lie within the window of the specific iteration. The size of the window is defined in terms of either the number of rows it contains or the date/time interval it covers.

Options

General Options

Row based

If this option is selected, both window size and step size (the distance between the starting point of one iteration and the starting point of the next) can be defined in terms of number of rows. With each iteration, the node then returns a table with the specified number of rows.

Time based

If this option is selected, both window size and step size (the distance between the starting point of one iteration and the starting point of the next) can be defined in terms of a date/time interval. If the window contains no row, it is moved forward using the step size until it contains at least one row or no rows are left. The chosen time column has to be sorted in ascending order or the node will fail (see Sorter node). Note that the size of the output table can vary from one iteration to the next, and that the loop terminates as soon as the last line of the input table appears in the window or in the step interval.

Window size

The window size is defined either as the number of rows it contains (row based) or as the date/time interval it covers (time based). Depending on the chosen method, the number of rows returned in each iteration is static or variable.

Step size

The step size is the distance between the starting point of one iteration and the starting point of the next. It is defined in terms of number of rows covered (row based) or time elapsed (time based).

Time column

Time column provides the column that shall be used in case of time-based windowing. Columns of type "Date", "Date&time", "Time", and "Date&time with zone" are supported. Missing values in the chosen column will be ignored. The chosen time column has to be sorted in ascending order or the node will fail (see Sorter node).

Start at

If this option is selected, the current point of time will start at the specified date and time. If this option is not selected, the current point of time will start with the date and time of the first row.

Advances Options

Limit window to table

If this option is selected, the window will be moved using the defined step size in such a way that it will not extend beyond the beginning of the table (if Backward or Central is selected) or beyond the end of the table (if Forward or Central is selected). (Note: rows at the start and the end may be omitted.)
If this option is not selected, undefined rows with missing values may be added at the end (if Forward is selected), at the beginning (if Backward is selected), or at the beginning and the end (if Central is selected) in order to guarantee a static window size.

Forward

If this option is selected, the current row will be the first row of the window when using row-based windowing. In the case of time based-windowing, the current point of time defines the temporal start point of the window.

Central

If this option is selected, the current row will be midway between the first and the last row of the window when using row-based windowing. In case of time-based windowing, the current point of time defines the the start and the end of the window in such a way that the temporal distance between the start of the window and the current point of time is the same as the temporal distance between the current point of time and the end of the window.

Backward

If this option is selected, the current row will be the last row of the window when using row-based windowing. In the case of time-based windowing, the current point of time defines the temporal end point of the window.

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