It was Sean Miller’s turn this week to set the challenge, which had an added twist – to complete only using the web authoring feature in Tableau Public, something I’d never tried before.

Most challenges use a version of Superstore Sales which I usually already have on my laptop, due to the multiple instances of Tableau Desktop installed, but this time, I had to get the data from data.world. I saved this locally then logged into Tableau Public online and started the process to build a viz online, by clicking the Create a Viz (Beta) option.

When prompted I then chose to upload from computer, the data source file I’d downloaded, and once done I was presented with the online canvas to start building

Unsure as to whether there was any auto save facility online, I decided to save the workbook pretty much immediately, although I was first prompted to navigate to the Data Source tab and create an Extract before I could save.

Now I was ready to start building out the requirements.

I started with the trend chart. The grain of the chart was at the month level, so I first created a specific field to store the Order Date at this particular level

Order Date Month

DATE(DATETRUNC(‘month’,[Order Date]))

I then added this to the Columns shelf as a continuous (green) exact date, and added Sales to the Rows shelf. I changed the mark type to Area, set the Colour to a blue, dropping the opacity to 50% in an attempt to match Sean’s colouring and adjusted the tooltip.

I then added another instance of Sales to the Rows shelf next to the existing one, changing the mark type of this instance to Line and setting the Colour to a darker blue at 100% opacity. I then used the context menu on this pill to set a Quick Table Calculation of type Moving Average.

By default this sets the average to the 3-month rolling average as per the requirement. I adjusted the tooltip, made the chart dual axis and synchronised the axis, then removed Measure Names from the Colour shelf that had automatically been added.

My next step at this point was to work on the filtering requirement. To help with this, the first thing I did was to Duplicate as crosstab (right click on the chart tab). This created a tabular view of the data so I could work on getting the calculations I need for the filtering. I flipped the columns and rows, so my starting point was as below.

I chose to use parameters to capture the min and max dates that the user selects on the dashboard.

pMinDate

Date parameter defaulted to 01 Jan 1900

And I also created pMaxDate exactly the same way.

I then needed fields to store the relevant dates depending on whether a selection had been made or not

Min Date Selected

IF [pMinDate]=#1900-01-01# THEN {FIXED : MIN([Order Date Month])}
ELSE [pMinDate]
END

The FIXED statement sets the date to the minimum month in the data set, if the parameter is set to its default. The below doed similar to get the maximum date in the data set.

Max Date Selected

IF [pMaxDate]=#1900-01-01# THEN {FIXED : MAX([Order Date Month])}
ELSE [pMaxDate]
END

Using these dates, I then created a field to determine whether the month was within the min & max dates

Is Month Selected?

[Order Date Month]>=[Min Date Selected] AND
[Order Date Month]<= [Max Date Selected]

Pop this field onto the table view, and show the parameters and set them to some other values eg Min Date = 01 Jun 2018 and Max Date = 01 Sept 2018. You’ll also need to adjust the table calc setting of the Moving Average Sales pill to compute by Is Month Selected as well.

You’ll see True is stamped against the rows which match the date range. Now, if you make a note of the Moving Average values against these rows, and then add Is Month Selected? = True to the Filter shelf, you should get just the True rows displaying, BUT the Moving Average values are now different. This is because, with this type of field as a filter, the filter is being applied BEFORE the table calculation is being applied – the table calculation essentially has ‘no knowledge’ of the rest of the rows of data as they have been filtered out. Solving this issue is the crux of this challenge.

Remove Is Month Selected? from the filter shelf. We’re going to create a new field to filter by instead

FILTER

LOOKUP(MIN([Is Month Selected?]),0)

This field uses the LOOKUP table calculation, and is basically looking at the value of the Is Month Selected? field in it’s ‘own row’ (denoted by the 0 parameter).

Pop this onto the table view, and you can see that it’s essentially a duplicate of the Is Month Selected? field.

Now add the FILTER =True field to the Filter shelf instead, and this time the rows will once again filter as required, but the Moving Average values will be the same as those in the unfiltered list, which is what we need.

This works because the field we’re filtering by is a table calculation. When added to the filter shelf, these types of fields are applied at the ‘end’ of the processing; ie the table calculation is computed against all the rows in the data AND THEN the filter gets applied. As a result the Moving Average values are retained.

This is all part of Tableau’s Order Of Operations and is a fundamental concept when working with filters.

Armed with this knowledge, we can now apply the FILTER=True to the Filter shelf of the chart we built.

Now we can start to work on the bar charts, which will show Sales along with Average Monthly Sales. For this 2nd measure, I need to work out the number of months captured between the min & max dates.

No. Months

DATEDIFF(‘month’, [Min Date Selected],[Max Date Selected])+1

And with this I can now create

Avg Monthly Sales

SUM([Sales])/MIN([No. Months])

The bar chart viz can then be quickly created by adding Sub-Category to Rows and both Sales and Avg Monthly Sales to Columns, and sorting by Sales descending. The colours of each bar are adjusted to suit.

The bars also need to react to the dates selected, but we can simply add the Is Month Selected? = True to the Filter shelf for this, as none of the values displayed on this chart are reliant on table calculations.

To remove the gridlines from both charts, select Format > Workbook from the menu, scroll down the Format dialog displayed on the right and set Gridlines to Off

Finally, title both sheets appropriately, and then add to a dashboard. We need to add 3 actions to this dashboard – 2 parameter actions and 1 filter action.

Create a parameter action which will on Select, set the pMinDate parameter by passing the Minimum Order Date Month, and will reset back to 01 Jan 1900 when unselected.

Then create another instance, which sets the pMaxDate parameter instead, passing the Maximum Order Date Month.

Finally, create a Filter Action which on Select of the bar chart, filters the trend chart

And with that, the challenge should be complete. My published viz is here.

Happy vizzin’! Stay Safe!

Donna