Explain the Table Calculation Function 'WINDOW_VARP(expression, [start, end])' in Tableau with Example?

 The WINDOW_VARP() function in Tableau is a table calculation function that calculates the population variance over a specified window or range of values. It measures the variability or dispersion of data points around their mean within the window.

The syntax for the WINDOW_VARP() function in Tableau is as follows:

WINDOW_VARP(expression, [start, end])

• expression: The field or calculation for which you want to calculate the variance.
• start (optional): The starting point of the window. If not specified, the window starts from the first data point.
• end (optional): The ending point of the window. If not specified, the window ends at the current data point.

Here's an example to demonstrate how to use the WINDOW_VARP() function in Tableau:

Suppose you have a dataset that contains information about the monthly sales of different products. You want to calculate the population variance of the sales values over a rolling three-month window.

1. Open Tableau and connect to your dataset.
2. Create a view that includes the "Date" field, the "Product" field, and the "Sales" field.
3. Right-click on the "Sales" field and select "Add Table Calculation."
4. In the calculation dialog box, choose "WINDOW_VARP" from the list of table calculation functions.
5. Specify the expression as the field or calculation for which you want to calculate the variance (in this case, "Sales").
6. Configure the specific settings for the WINDOW_VARP function, such as the addressing and partitioning options, to define the three-month rolling window.
7. Click "OK" to apply the WINDOW_VARP function to the sales values.

Tableau will calculate the population variance of the sales values over the specified rolling three-month window. The variance represents the average of the squared differences from the mean, indicating the spread or variability of the sales values within the window.

You can further customize the view, apply sorting, or add additional calculations based on the calculated population variance. For example, you can create a visualization that shows the trend of the variance over time or compare the variances across different products.

The WINDOW_VARP function allows you to perform calculations related to population variance within a specified window. It helps you understand the variability and dispersion of values within a dataset and supports data analysis and visualization based on these measures.