This type of question, ‘How do I show prior month when using a month filter?’, ‘My Year on Year is blank when I filter?’, appears A LOT on the Tableau forums.
There are two main ways to show the prior period / keep a previous value for prior period comparison.
1. Use a Parameter to keep a prior period
- Create a parameter to enable selection of a month/year
- Create a calculated field to use this parameter to filter the data – for example:
DATETRUNC('month',DATEADD('month',1,[DateField])) >= [MonthParameter] OR DATETRUNC('month',[DateField]) = [MonthParameter]
- Drag the calculated field to the filter shelf and set to True
2. Build a Tableau Late Filter
This is most useful when wanting to show a MoM change or a YoY change.
A standard filter removes the prior value from the data so the MoM or YoY is blank.
One of the last things to calculate in Tableau, based on Tableau’s Order of Operations, are table calculations.
Therefore the Month on Month (or Year on Year) calculates first, then the table calculation filter is applied, the MoM/YoY calculation remains good.
How to build a late filter in Tableau
- Create the calculation to get the value for the prior period:
LOOKUP(SUM([Sales),-1) - Create a calculated field to be the month filter. This has to be a table calculation to happen after the calculation of the prior period:
LOOKUP(ATTR([DateField]),0) - Drag the month calculated field to the filter shelf and Show Filter.
Both of these options have pros and cons, which is better for you depends on the specific requirements. For example a parameter filter doesn’t allow multi-select and can’t ‘Show Relevant Values’. A table calculation filter can only apply to a single worksheet so provides limited use in a dashboard if intended to drive multiple worksheets.
Examples keeping the prior period in the calculation
Both examples are using the Sample Superstore EU data source. Both are set up the same, using a Quick Table Calculation doing Percent Difference and using the default settings. We’re returning the month on month change.
Tableau Parameter Filter example
- Create a parameter, MonthParameter, based on the Order Date field. Format to month and year: mmm yy.
- Create a calculated field, MonthFilter, to use that parameter as a filter. Note the usage of DATETRUNC. This pushes any date to the 1st of the month. Therefore Order Dates of 15 Aug would be converted to 1 Aug.
[MonthFilter]: DATETRUNC('month',[Order Date])>=DATEADD('month',-1,DATETRUNC('month',[MonthParameter])) AND DATETRUNC('month',[Order Date]) <= DATETRUNC('month',[MonthParameter])
- Drag the MonthFilter to the filter shelf and set to True.
Tableau Lookup Late Filter
- Create a calculated field to use as the month filter
[MonthLateFilter]: LOOKUP(ATTR(DATETRUNC('month',[Order Date])),0)
- Use DATETRUNC so all order dates within a month are set to the 1st of that month – i.e. they all share the same date. Table calculations have to be an aggregation, therefore we have to use ATTR as it’s most appropriate for this use case. However this will only work if all the dates for a month/year are the same. Different dates within a month would return a *, which is no good for the filter.
- Set the Default Properties – Date Format to Custom mmm yy
- Drag the field from Measures to the Filter shelf.
The workbook with these examples is available on Tableau Public.