Can you create a moving average chart with a focus on selected subcategories?

Following the #WOW survey where practice in table calculations was the most requested feature, Lorna continues with the theme in this challenge, where the focus is on the moving average table calculation, plus a couple of extra features thrown in.

Moving average

This is based on the values of data points before and after the ‘current’ point, as defied by the parameters which will need to be created.

pPrior

Integer parameter ranging from 1 to 6 and defaulted to 3. You need to explicitly set the Step size to 1 to ensure the step control slider appears when you add the parameter to the dashboard. This will be used to define the number of data points prior to the current to use in the calculation.

Create an identical parameter pPost to define the number of data points to use after the current one.

With these parameters, we can now create the core calculation

Moving Avg

WINDOW_AVG(SUM([Sales]), (-1*[pPrior])+1, [pPost])

As the requirement states that the ‘prior’ parameter needs to include the ‘current’ value, then we need to adjust the calculation – ie if the parameter is 3, we actually only want to include 2 prior data points, as the 3rd will be the current point itself. This is what the +1 is doing in the 2nd argument of the function.

Lorna has stated that 3 Sub-Categories are grouped to form a Misc category, so we need to create a group off of Sub-Category (right click Sub-Category -> Create -> Group).

Multi-select the 4 options that need to be grouped (hold down Ctrl as you select), and then group, and rename the group Misc.

Now we can check what the calculation is doing. If you add the fields onto the view as below, and set the Moving Avg table calculation to compute using Month of Order Date only (see further below), you should be able to see that each month’s moving avg value is calculated based on the sales value of the set of previous & post months as defined by your parameters. In the image below the Moving Avg for Accessories in June 2018, is the average of the Sales values from April 2018 – Sept 2018.

With this you can start the beginnings of the viz – don’t forget to set the table calc as above.

Colouring the lines

This will be managed by using a set.

Right click on the Sub-Category (group) field -> Create -> Set. Initially select all values. Add this field to the Colour shelf. Additionally, click the Detail symbol (…) to the left of the Sub-Category (group), and select the Colour symbol, so this field is also added to the Colour shelf.

The resulting colour legend will look something like this
Edit the colour legend, then choose Hue Circle and select Assign Palette to randomly assign colours to all the options

To show the set values, click on the context menu of the Sub-Category (Group) field on the Colour shelf, and Show Set.

This will add the list of options for selection

Uncheck All so none are selected, which will change the colour legend to read ‘Out, xxx’. Edit the colour legend again, and control-click to multi select all options, then set to a single grey

Now if you select a few options, the ones selected will be coloured, while the others remain grey

Additionally add the set field onto the Size shelf and make the In option bigger than the Out.

Shading the background

For this we need to create an unstacked area chart with one measure representing the maximum moving average value for the month, and the other representing the minimum moving average value for the month. We’ll need new calculated fields for this:

Window Max Avg

WINDOW_MAX([Moving Avg])

Window Min Avg

WINDOW_MIN([Moving Avg])

If you’ve still got your data sheet available, then move Sub-Category (Group) onto Rows, then add the two newly created fields.

In this case there are ‘nested’ table calcs. You need to ensure the setting related to the Moving Avg is computing by Month Order Date only, but the setting related to the Window Max Avg (or Window Min Avg) is computing by Sub-Category (Group).

If set properly, you should see that for each month the max / min values are displayed against every row.

Back to your chart viz sheet, and add Window Max Avg to Rows. Set the table calc settings as described above, then remove the Sub-Category (group) Set field from the Colour shelf of this measure, and change the Sub-Category (group) to be on the Detail rather than Colour shelf.

Change the mark type to Area, set the Opacity of the colour to 100% and set stack Marks to be Off (Analysis Menu -> Stack Marks -> Off).

Now drag Window Min Avg onto the Window Max Avg axis and drop it when the ‘2 columns’ image appears.

This will change the view so Measure Values is now on the Rows shelf and Window Min Avg is now displayed in the Measure Values section on the left hand side.

Adjust the table calc setting of Window Min Avg to be similar to how we set the Max field. And now drag the fields so Window Min Avg is listed before Window Max Avg. Measure Names will now be on the Colour shelf of this marks card, so adjust so Window Min Avg is white and Window Max Avg is pale grey.

Now make the chart dual axes, synchronise the axes, and set the Measure Values axis to the ‘back’.

Everything else is now just formatting and adding onto a dashboard. My published viz is here.

Happy vizzin’! Stay Safe!

Donna

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