This week’s challenge, set by Lorna, made use of the newly released ‘dotted line’ format in v2023.2, so you’ll need that version in order to achieve the dotted line that spans the 2 marks being compared. If you don’t have this version, you can still recreate the challenge, but you’ll just have a continuous line.

Building the calculations

This challenge involves table calculations, so my preferred startig point is to build out all the fields I need in a tabular format.

So start by adding Category to Columns and Order Date at the discrete (blue) week level to Rows. Add Sales to Text (I formatted Sales to $ with 0 dp, just for completeness).

Apply a Moving Average Quick Table Calculation to the Sales pill, then edit the table calculation to it is averaging over the previous 5 values (including the current value – ie 6 weeks in total), and it is computing by Order Date only.

Add another instance of Sales back into the table, so you can check the values.

The ‘moving average’ Sales pill is what will be used to plot the main line chart.

But we need to identify 2 points on the chart to compare – the values associated to a start date determined by the user clicking on the chart, and the values associated to an end date determined by the user hovering on the chart. We’ll make use of parameters to store these dates

pDateClick

date parameter defaulted to 27th Dec 2020

pDateHover

date parameter defaulted to 28 Nov 2011

We can then determine what the moving average Sales values were at these two dates

Sales to Compare

IF DATETRUNC(‘week’, MIN([Order Date])) = [pDateClick] OR DATETRUNC(‘week’, MIN([Order Date])) = [pDateHover] THEN
WINDOW_AVG(SUM([Sales]), -5, 0)
END

Add this to the table, and the values for the moving average will only be populated for the two dates stored in the parameters

This is the field we will use to plot the points to draw the lines with.

But we also need to work out the difference between these values so we can display the labels.

Sales to Compare Start

WINDOW_MAX(IF DATETRUNC(‘week’, MIN([Order Date])) = [pDateClick] THEN WINDOW_AVG(SUM([Sales]), -5, 0) END)

If the date matches the pDateClick (start) date then return the moving average and then spread that value over every row.

Sales to Compare End

WINDOW_MAX(IF DATETRUNC(‘week’, MIN([Order Date])) = [pDateHover] THEN WINDOW_AVG(SUM([Sales]), -5, 0) END)

If the date matches the pDateHover (end) date then return the moving average and then spread that value over every row.

Add these into the table, and you can see how the table calculations are working

The moving avg value for the start date is displayed in every row against the Sales to Compare Start column, while the moving avg for the end date is displayed in every row for the Sales to Compare End column.

With these values now displayed on the same row, we can calculate

Difference

[Sales to Compare End]-[Sales to Compare Start]

formatted to $ with 0 dp

and

% Difference

[Difference]/[Sales to Compare Start]

formatted to a custom number format of ▲0.0%;▼0.0%;0.0%

Popping these into the tables, the values populate over every row, but when it comes to the label, we only want to show data against the comparison date, so I created

Label Difference

IF DATETRUNC(‘week’, MIN([Order Date])) = [pDateHover] THEN [Difference] END

formatted to $ with 0 dp, and

Label Difference %

IF DATETRUNC(‘week’, MIN([Order Date])) = [pDateHover] THEN [% Difference] END

formatted to a custom number format of ▲0.0%;▼0.0%;0.0%

With all these fields, we can now build the chart

Building the viz

On a new sheet, add Order Date set to the continuous (green) week level to Columns and Category to Rows. Add Sales to Rows and apply the moving average quick table calculation discussed above, adjusting so it is computing over 5 previous weeks and by Order Date only

Add Category to Colour and adjust accordingly, then reduce the opacity to around 40%

Add pDateClick to Detail then add a reference line to the Order Date axis the references this field. Adjust the Label and Tooltip fields, and set the line format to be a thick grey line.

Format the reference line text so it is aligned top right.

Then add pDateHover to Detail and add another reference line, but this time set the line so it is formatted as a dashed line.

Next, add Sales to Compare to Rows. Adjust the colour of the associated marks cards so it is 100% opacity.

Right click on the Sales to Compare pill and Format. On the Pane tab on the left hand side, set the Marks property of the Special Values section to Hide (Connect Lines). Click on the Path shelf and choose the dashed display option.

Set the chart to be Dual axis and synchronise the axis. Remove Measure Names from the All marks card. Hide the right hand axis.

Add Label Difference and Label Difference % to the Label shelf. Set the font to match mark colour and adjust font size and positioning. I left aligned the font but added a couple of spaces so it wasn’t as close to the line. I also added a couple of extra carriage returns so the text shifted up too.

Finally adjust tooltips, remove column dividers and hide the Category column title. Adjust the axis titles.

Adding the interactivity

Add the sheet onto a dashboard, then add 2 parameter actions

Set Start on Click

On select of the Viz sheet, pass the Order Date (week) into the pDateClick parameter. Leave the current value when selection is cleared (ie when user clicks elsewhere in viz, but not on another mark).

and

Set Comparison on Hover

On select of the Viz sheet, pass the Order Date (week) into the pDateHover parameter. Leave the current value when selection is cleared (ie when user clicks elsewhere in viz, but not on another mark).

And that should be it.

My published viz is here.

Happy vizzin’!

Donna