Candra set this seasonal fun challenge this week. It may not deliver data visualisation best practice, but as a ‘seasoned’ #WOW participant, this provided a chance to use a technique I rarely use (background images) and learn a brand new technique (colouring a bar chart with a gradient).

Getting set up

To start you’ll need to download all the files Candra provided, which will consist of the data (across 2 sheets) and 3 images.

The bauble and star image will need to be saved into your Tableau Shapes repository – I copied them into a new folder I called Xmas in this directory ..\My Tableau Repository\Shapes

The tree image just needs to be saved somewhere you’ll remember.

Building the Tree Chart

Connect to Sheet1 of the downloaded WOW Advent Calendar excel file.

Drag X to Rows and Y to Columns and disaggregate the marks (Analysis -> uncheck Aggregrate Measures)

You should get the basic layout of where the baubles are positioned. You may also notice that the X & Y values in the dataset were labelled wrong. The x-axis is your horizontal axis, but these have been stored in the Y field, while the vertical y-axis values have been stored in the X field. You may wish to rename these to save you getting confused.

Add Day to the Label shelf, and align middle centre.

We need to distinguish the bauble marks from the star mark. The star mark has a NULL value for the Day field, so we can utilise that

Day Is NULL

ISNULL([Day])

Add this onto the Shape shelf, and adjust the shape images to source the new images you saved into your shapes repository (if you can’t find them try clicking ‘reload shapes’). Adjust the initial size of the images via the slider on the Size shelf.

Now add Day Is Null to the Size shelf too. Edit the size and adjust the mark size range to suit, so the star is larger than the baubles.

Adjust the Label of the bauble so the text is larger and white.

To make the tooltip slightly more readable than that in the provided solution, I created my own custom version

Tooltip

IF [Day is Null] THEN “It’s Christmas Day!”
ELSEIF [Day]=1 THEN STR([Day]) + ” day until Christmas”
ELSE STR([Day]) + ” days until Christmas”
END

Add this to the Tooltip shelf, and adjust so it’s just referencing this field.

Add Link to the Detail shelf – this will be needed for the interactivity later.

Now we’ll add the background image via the Maps -> Add Background Image -> <datasource> menu option. Click to add image, then browse to where you’ve saved the Xmas tree image.

We need to define the min/max coordinates for where the tree image should be positioned, and based on this, we want the horizontal X axis (the Y field) to range from 0-4 and the vertical Y axis (the X field) to range from 0 to 6. Press the Apply button and you see whether things look to be placed correctly before you close all the dialog windows.

Next we need to fix the axis, so that when interacting later, we keep the whole tree visible. The vertical axis should be fixed from 0-7, and the horizontal axis should be fixed from 0 to 4.

Then we need to remove all the axis from displaying (uncheck show header), and all row/column borders and gridlines and axis rulers.

The final step is to remove the map options from displaying when you hover over the chart – Map ->Map Options and uncheck all the options displayed in the dialog

Building the Gradient Coloured Bar Chart

Candra provided a hint in her instructions pointing to the Flerlage Twins blog. A quick search on the site for the keyword ‘gradient’, and I landed on this post from 3 years ago https://www.flerlagetwins.com/2019/02/gradient-colors.html.

Since the process is already documented, I don’t have to write all the steps out myself 🙂 I’ll just point out the fields I used/created, since we’re working with a different data set.

Firstly I created a new data source for this chart, which combined Sheet1 with the Range sheet, and used a relationship calculation of 1 = 1 to combine the data (Relationships didn’t exist when the blog post was written).

The equivalent of the Sales Adjusted field is the existing pre-computed Sheet1(Count) field, so we don’t need any calculated field for this.

Max Segments in my solution is

Max Range

WINDOW_MAX(MAX([Range (Range)]))

Note – Range (Range) is referencing the Range field from the Range table. If you just drag the field into the calculation window, it will automatically present in this way.

Total in my solution is

Total Count

TOTAL(COUNT([Sheet1]))

Size in my solution is

Size

[Total Count]/[Max Range]

and finally Color in my solution is

Colour

([Max Range]-[Index]) * [Size]

Add Challenge Year to Rows (rather than Category), change the mark type to bar if it doesn’t change automatically. Reverse the axis so 2018 is listed at the top, then change the Challenge Year pill to be discrete (blue) rather than green.

If you follow the other blog post through, you should hopefully end up with

You then need to show the labels and adjust the tooltip against the CNT(Sheet1) marks card only.

As before, remove all gridlines borders etc.

Adding the interactivity

Add the 2 sheets to a dashboard. We need to allow the tree to filter on click of the bar chart. I used the ‘use as filter’ option on the context menu of the the bar chart object to quickly set this.

This adds a filter action to the dashboard, but is a quick way of getting it created rather than having to manually set it up via the dashboard -> actions menu.

I did use this menu though to add the URL action to the Tree sheet, which just needs to reference the Link to the Challenge field.

So a relatively short blog this week, since the most complicated section is already written up be Ken Flerlage (thanks Ken!). It was a great fun little challenge, which still allowed for plenty of learning opportunities. My published viz is here.

Happy vizzin’! Stay Safe!

Donna