Waterfall Chart

[hughess]

A waterfall chart is great for showing decomposition of changes.

I've had a start at creating one (which I will open in a draft PR for those who are interested in taking a look).

Considerations for implementation

• Axis labels are important on these charts and will often be long strings - the chart needs to be able to handle multi-line labels without cutting off characters or breaking words apart
  • I think it probably needs "breaking" behaviour by word, followed by either truncation (...) or expansion of the chart size
  • This will also need to work well responsively and on mobile
• We don't currently have multi-line axis labels in our other charts - this will need some thinking to make sure the chart area is the right size in all cases. Currently, adding multi-line axis labels shrinks the main chart area
• The initial attempt I've made requires a specific data format:
  • category - category to use on x-axis
  • value - change to show on chart
  • total - boolean - should this be treated as a total/subtotal on the chart
• The SQL required to get data into this format can require a lot of work. We might want to offer other alternatives for the structure of the data getting passed in
  • I don't think this would change the implementation within echarts - we could just add a layer of logic above this to get it into the format echarts requires
• Data labels should be included - positioning these may be difficult
• I haven't thought about tooltips yet. I'm thinking they will be straightforward though - probably a config override sent from Waterfall to Chart
• Subtotals - the logic for generating the chart series will need to be updated to accomodate subtotals - currently, having a total in the middle of the data throws off the cumulative sum
• We may want to offer sorting - e.g, sort by magnitude of change. This shouldn't be hard to do with this data format since we can easily identify the totals and exclude them from sorting
• In a lot of cases, people need to start the y-axis at a higher number than 0 to make the changes visible enough on a waterfall chart
  • We could offer a yMin prop to allow someone to set it manually
  • I could also imagine some dynamic logic to check the change range (max of cumulative sum - min of cumulative sum) as a % of axis range and adjust the yMin so that the change range takes up something like 50% of the vertical chart area

[matsonj]

The SQL required to get data into this format can require a lot of work. We might want to offer other alternatives for the structure of the data getting passed in

I think including a sample SQL query in the documentation would go a long way. It is indeed fairly complex but you can simplify it massively with clever windowing (LAG / LEAD or cumulative sums). I think having a clean example of the data model on this one is key because it always takes me like an hour in power BI to get these right.

[archiewood]

@matsonj Does the below interpret what you are saying correctly?

There are a few common uses for waterfalls, for example

• Revenue bridge (by category, geography etc)
• Volume value bridge (revenue start, impact of price, impact of volume, impact of mix, residual, revenue end)

We should write an example of how to wrangle a standard table format in order to do a waterfall of the above types

eg

Assuming your columns are this:

• date, revenue, category
• Then use this example query to get into waterfall format

Assuming your columns are this

• date, item, price, quantity, [total revenue]
• Then use this other query

And as a follow up question: what are your most typical waterfall use cases (assuming not covered by the above two)?

[matsonj]

@archiewood yeah, I think those are the core cases. I think the core questions I usually run into that usually are answered best with waterfalls are the following:

• Why did revenue change this month vs last in percentage and absolute $? (i.e. change in revenue by type - recurring, churn, growth, etc)
• Why did profitability change this month vs last month in percentage and absolute $? (i.e. contribution margin by product line)

Could go down the line on any GL line item too, but those are the two that seem the most frequent in my exp.

[rasmusengelbrechtsorensen]

Is Waterfall still on the Backlog, or is it closed for now? 😊

[hughess]

Still on the backlog, would definitely welcome contributions!

[rasmusengelbrechtsorensen]

Awesome! Unfortunately, I don't think I have the abilities to contribute... 😅