Community month for the #WOW2022 team continued this week, with Liam Huffman setting this challenge to build a year on year comparison chart with twist.

Typically when building YoY charts you compare the month from last year with the same month this year, or a week from last year with this year (eg week 3 2021 v week 3 2022), or a specific date last year with this year (eg 4th March 2021 with 4th March 2022). However for this challenge, the focus was on being able to compare based on equivalent weekdays (at least that’s what I understood from reading). By this I mean if 10 October 2022 is a Monday, that needs to be compared with the equivalent weekday in the previous year. 10 October 2021 was a Sunday, so we actually need to compare Monday 10 Oct 2022 with Monday 11 Oct 2021.

So that’s the direction I took with this challenge, but in doing so couldn’t get the numbers to exactly match with Liam’s solution. Unfortunately I just couldn’t get my head around Liam’s approach even after looking at it. So I’m blogging this based on my interpretation of the requirement, which may be flawed.

Baselining the Dates

When building YoY charts like this which need to be flexible based on the date part selected, you need to ‘baseline’ the dates; well that’s the term I use, others might refer to it as normalising. Ultimately you need to get the dates that span multiple years to all align to the same year, so you have a single x-axis that just spans a single year.

Now based on what I talked about above, its not just a case of changing the year of every Order Date to match for all the records, we need to find the equivalent weekday from the previous year and align that.

To do this I first created a parameter

pToday

date parameter defaulted to 10 Oct 2022

This is simply to provide a constant end point. In a business scenario when the data changes, any reference to pToday would just use TODAY().

I then created

1st Day of Current Year

DATE(DATETRUNC(‘year’, [pToday]))

This returns 1st Jan 2002

I then worked out what weekday this was

Weekday of 1st Day Current Year

//determine the day of the week this year started on, based on todays date
DATENAME(‘weekday’, [1st Day of Current Year])

This returns Saturday

I then wanted to find the date of the first Saturday in every year, but firstly I needed to determine the weekday for each Order Date

Weekday

DATENAME(‘weekday’, [Order Date])

Date of 1st weekday Per Year

//get the first date in each year which falls on the same weekday as the first day of the current year
//ie 1st Jan 2022 is a Saturday. This is day 0 for 2022. We need to find day 0 for every other
//year, which is the date of the first Saturday in that year

{FIXED YEAR([Order Date]): MIN(IF [Weekday]=[Weekday of 1st Day Current Year] THEN [Order Date] END)}

For each year, get all the dates which fall on a Saturday, then returned the earliest one of those.

Popping all this information out in a table, we can see that in 2019, the first Saturday in the year was 5th Jan 2019, so all the records for dates in 2019 are stamped with 5th Jan 2019.

This Date of 1st weekday Per Year is essentially day 0 for each year. We now need to record a number against each day in the year

Days From Date

//get the number of days from the date of 1st weekday per year
DATEDIFF(‘day’, [Date of 1st weekday Per Year], [Order Date])

And with this number, we can now record the equivalent date in 2022 against each date

Baseline Date

//need to normalise all dates for every year to the current year,
//ie Day 0 for every year = 01 Jan 2022

DATE(DATEADD(‘day’, [Days from Date], [1st Day of Current Year]))

Add these fields into the tabular view and you should hopefully see how this is working

Building the Line Chart

We need some additional parameters to help build the chart.

pDatePart

string parameter defaulted to Month, with 3 values listed as shown below

pStartDate

date parameter set to use the 1st Day of Current Year when the workbook opened, meaning current value was 1st Jan 2022

pEndDate

date parameter set to use the pToday parameter when the workbook opened, meaning current value was 10th Oct 2022

With the pDatePart field, we need to define the actual date we’re going to plot

Date to Plot

DATE(DATETRUNC([pDatePart], [Baseline Date]))

when this is set to week, the date for all days in the same week are set to the first date in the week. Similarly, when this is set to month, all dates in the same month are set to 1st of the month.

The data also needs to be filtered based on the start & end dates selected, so we need

Dates to Include

[Baseline Date]>= [pStartDate] AND [Baseline Date]<=[pEndDate]

Add this to the Filter shelf of the tabular view and set to True. Also add Date to Plot into the table, and show all the parameters. Change the dates and the date part field and familiarise yourself with how the parameters impact the data.

Now we’re happy we’ve got all the key fields we need, then create a new sheet, show the parameters and add Dates to Include = True to Filter.

Then add Date To Plot as an exact date continuous (green) pill to Columns and Sales to Rows.

Create

Order Date Year

YEAR([Order Date])

and add to Colour. Adjust the colours accordingly.

Format the Sales axis, so the numbers are displayed as numbers rolled up to thousands (k) with 0 dp. Edit the Date to Plot axis to remove the title, then format the dates displayed to be in dd mmm custom format. Remove all gridlines and zero lines. Only axis lines should be displayed. Update the title.

Add Date to Plot to Tooltip as a discrete attribute (blue pill). Add MIN(Order Date) to Tooltip too. Adjust tooltip wording to suit.

Building the bar chart

Add Order Date Year to Rows and Sales to Columns. Sort Order Date Year descending.

Add Order Date Year to Colour. Adjust the opacity to about 50% and add a border. Widen the rows. Add Sales to Label and format label to be $K to 1 dp.

Add another instance of Sales to Detail, then adjust to use a Quick Table Calculation of Percent Difference. Move this pill from Detail to Label. Adjust the table calculation so it is relative to Next rather than previous

Format the Sales field that has the table calc, so it is custom formatted to ↑ 0.0%; ↓ 0.0%

Modify the label so the % change is in ( ) .

Add MIN(0) to Columns (type directly in to the columns shelf). Remove the two Sales fields from the marks card, and add another instance of Order Date Year to the Label shelf. Adjust the Label so the font is larger, matches mark colour and is rotated.

Make the chart dual axis, and synchronise axis.

Turn off all tooltips, hide the Order Date Year column and both axis. Remove all gridlines and row & column borders. Add a title. Remove any instance of Measure Names that may have been added to the Colour shelf of either marks card.

And add Dates To Include = true to the Filter shelf.

Adding the interactivity

Add the sheets onto a dashboard and adjust the layout to match. I floated the parameters and positioned with some floating text boxes too, to get the desired display.

Add a highlight dashboard action

Highlight Trend

which on hover of the bar, highlights the trend line via the Order Date Year field only.

To manage the filtering of the bars, I decided to use a parameter action, by passing the date related to the point selected. For this I created

pDateHovered

I used a string parameter, so I had a value I could use to reset to

I then needed to create an additional field

Date to Plot String

STR([Date to Plot])

and I added this to the Detail shelf on the trend sheet. This needs to be set to be an attribute, so the lines remained joined up.

Additionally I needed

Filter On Hover

[pDateHovered] = ” OR [Date to Plot] = DATE([pDateHovered])

which I added to the Filter shelf of the Bar chart sheet and set to true.

Then back to the dashboard, create a parameter action

Filter Bars

which on hover on the trend chart, updates the pDateHovered parameter passing through the Date To Plot String field, and resets back to <empty string> when released.

And that should be it… my published viz is here.

Happy vizzin’!

Donna