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Debugging Complex Calculations
- 2. Debugging Complex Calculations Austin Dahl Director of Engineering, Analytics Mrunal Shridhar Commercial Presales Lead, EMEA
- 7. • Know row-level granularity of your data • Know what makes each row unique The dimension fields represent the LOD of the data source. You cannot drill down further than this.
- 8. Totally Aggregated Totally Disaggregated (granularity of data source - cannot go lower) Dimensions determine the Viz LOD. The Viz LOD becomes less aggregated/more granular as more dimensions are added. Granularity Less More Aggregation More Less # # # # # # # Dimensions Measures
- 11. Do you have all the dimensions? No need to derive new dimensions New dimension need to have a subset of data only? Subset of data need to update automatically? Create a computed conditional set Create a manual set Dimension need to be derived at row level? Create row-level calculation Create FIXED LoD expression
- 12. Measure needs mixed level of aggregation? Break measure into sub- measures with a fixed level of granularity? Go back to Step 1, and go through the process for each sub-measure Measure level of aggregation same as dataset granularity? Create a row level calculated field Measure aggregation at the same LoD as the viz LoD? Create an aggregated calculated field Measure aggregation more granular than viz LoD? Does result need just one mark/value? Create FIXED or EXCLUDE LoD expression Create table calculation Create INCLUDE LoD expression Aggregation Granularity
- 15. discount category Measure needs mixed level of aggregation? Break measure into sub- measures with a fixed level of granularity? Go back to Step 1, and go through the process for each sub-measure Measure level of aggregation same as dataset granularity? Create a row level calculated field Measure aggregation at the same LoD as the viz LoD? Create an aggregated calculated field Measure aggregation more granular than viz LoD? Does result need just one mark/value? Create FIXED or EXCLUDE LoD expression Create table calculation Create FIXED or INCLUDE LoD expression Aggregation Granularity
- 16. discount product category Measure needs mixed level of aggregation? Break measure into sub- measures with a fixed level of granularity? Go back to Step 1, and go through the process for each sub-measure Measure level of aggregation same as dataset granularity? Create a row level calculated field Measure aggregation at the same LoD as the viz LoD? Create an aggregated calculated field Measure aggregation more granular than viz LoD? Does result need just one mark/value? Create FIXED or EXCLUDE LoD expression Create table calculation Create INCLUDE LoD expression Aggregation Granularity
- 24. Dropping dimensions on these shelves adds them to the Viz LOD.
- 29. • It is easy for you to create a ton of LoD expressions • It is very easy to overwhelm your data model • It is most easy to use a wrong LoD expression in your viz
- 33. Extract Filters Data Source Filters Context Filters FIXED Expressions Evaluated Dimension Filters INCLUDE/EXCLUDE Expressions Evaluated Measure Filters Local Filters (ATTR, geocoding) Table Calc Filters Hide database local
- 35. Query • Query database • Cache Results Data • Local data joins • Local calculations • Local filters • Totals • Forecasting • Table calculations • 2nd pass filters • Sort Layout • Layout views • Compute legends • Encode marks Render • Marks • Selection • Highlighting • Labels
- 48. NULL
- 52. What can go wrong? Join Some rows might not match. What will happen? Join There might be more than one match. Will you count things twice? Left It’s asymmetric, do you have the right primary? Post- aggregate It’s already aggregated, is the combination of aggregates valid?
- 61. Please complete the session survey from the Session Details screen in your TC16 app
Editor's Notes
- Demo from workbook what these tools are and how they can help
- No demo Now that you know what dimensions are needed to answer your analytical question. First step is to ensure that you those dimensions. Use this framework to ensure that you have them. Options include: Sets – manual or computed. Row level calculation LoD expression (Fixed) The reason we didn’t use filter and instead a set is because when you filter you exclude those values and cannot be used in a calculation.
- Show a couple of examples of us working through the framework
- Show a couple of examples of us working through the framework
- Show a couple of examples of us working through the framework
- Demo building table calculations in v9.3 using index() and then the new improvements in v10
- Demo building table calculations in v9.3 using index() and then the new improvements in v10
- Demo building table calculations in v9.3 using index() and then the new improvements in v10
- Show a quick example, for dimension or measure, and for filtering on fixed LoD
- Add comments to calculations Add comments to field by copying desc
- Demo % of Total
- Examples to discuss: Font – layout views Filter – query but could be data if it is a table calculation or 2nd pass Marks – when you select a mark it is simply render but when you have action filters you could trigger the whole pipeline. Show an example of interactive vs. non-interactive interaction
- One of the big ideas I want you to understand is you can use the techniques of visualization to make your job of debugging easier and faster. To do this I’m going to take an example from Mrunal’s LOD expressions.
- A few minutes ago, Mrunal was making sure that his calc for profit ratio on categories matched with the total calculation for profit ratio. I’m going to build a visualization that shows both the new calc and the total. If they align I know the calc is correct. Do they align? Yes. The calc is what I was expecting. In this case, I was only trying to see if three numbers match, but the technique of using a visualization will scale up. If there were 5 or 15 or 500 categories, I could tell in a glance if there was a difference between the bar and the reference line.
- The next section is about joins.
- In a normal join operation, you start with the columns on the left and augment them with columns from the right where you have a match on the join key. In this example, the data set on the left has Sales for each State and the data set on the right has Population for each state. When I join them by state, I’m going to end up with State, Region, Category, Sales and Profit, as well as Time Zone and Population. For the first two rows, California, the data I get in Time Zone and Population is West and 38 million something. Similar things happen for Colorado and Illinois. For Missouri, Montana and Nevada, there’s just one row each. For Texas and Washington it’s two rows each.
- I can build a map of the sales per region. BTW, do you know how to create custom territories from existing geographic fields?) Right click on the field, Geographic Role Create From Select the appropriate field. I can easily build a map of sales per time zone. Cool, my join added something useful data.
- Let’s build another viz. How many potential customers are there in each state? Wait! How can that be? There are only 38M people in California. What’s going wrong?
- Remember as part of the join, population gets put in to two rows for California. When I drag out population, the default aggregation is SUM. So my viz, which is doing an aggregation by state sums all the Population for each state. That’s wrong for 5 of the 8 states in this data set.
- How would I detect this might be a problem? Do a sanity check, and make it easy for yourself. You can add reference lines. You can build a dashboard with the original viz.
- You might be tempted to use a different aggregation, but you will need to sanity check it repeatedly. LODs usually work nicely. Blending is almost magical in how it works. It very often does exactly what you want.
- Another concern with Joins are Nulls. When you do a left or a right join there can be Nulls. In this case, if I do a left join the row for Oregon will get NULL, for Region, Category, Sales and Profit. If I do an inner join, I don’t even get a row for Oregon, but let’s stick to left joins for now.
- Let’s look at Sales for the time zone.
- If I didn’t already know there were NULLs for Oregon, how might I find out? I can build a bar chart to look at how many records there are. I can build a heat map to see where the NULLs are. This works well even when there are lots and lots of records. As you are looking, there are questions you can ask yourself.
- Blends are a post aggregate left join. An aggregate of aggregates is sometime fine. A sum of sums is valid. A min of mins is valid. A average of sums is not the same as the average of the underlying items. An average of averages is not either, but it’s often close and can fool you easily.
- Here’s an example that I was involved with. You may ask why different data sources? Because I didn’t have control of all of them. They were from different departments. You may ask why I didn’t use a cross data base join? Because when I started this, Tableau didn’t have the features.
- These are my motivations. How can I check for dirty data? How can I check my assumptions?
- I’ve been talking about blends for a while, but there are similar concepts that apply to joins. Most of the time, you don’t expect many-to-many joins and most of the time they are not the right thing. However, sometimes the data surprises you and you get some unexpected joins. In the Intern example, I did not expect Stephanie to have to mentor two interns. Here’s is an example to detect that in the join case.