The excellent work that David Eldersveld has been doing recently on using SVG images in Power BI has generated a lot of interest; now that the August 2018 release of Power BI Desktop allows you to set data categories on measures – and specifically the Image URL data category – David has been able to apply his work to the creation of sparklines and small multiples in Power BI. He’s already published an example in the Quick Measures gallery here; you might also want to check out this blog post and quick measure by Tom Martens too.
All this got me thinking: what if there was a simple web service that could generate charts, one that didn’t need any authentication, could work with simple GET requests and was free to use? Well guess what, there is one created by Google: the Google Image Charts API. It turns out that it makes it super easy to create sparklines and small multiples in Power BI with very little DAX needed.
Here are two examples of what’s possible with some simple DAX in a measure:
Both examples use data from a table called Sales with the following contents:
The first example, the Sales Sparkline measure, has the following definition:
Sales Sparkline = var BaseURL = "https://chart.googleapis.com/chart?" var ChartType = "cht=ls" var ChartScale = "&chds=0,10" var ChartSize = "&chs=150x150" var SeriesColour = "&chco=000000" var ChartData = "&chd=t:" & CONCATENATEX(Sales, Sales[Sales], ",", Sales[Month]) return IF( HASONEVALUE(Sales[Product]), BaseURL & ChartType & ChartScale & ChartSize & SeriesColour & ChartData )
All I’m doing is building up the URL to call the API from the parameters listed here. The second measure is basically the same as the first, but the chart type is driven by a selection in a slicer. It’s not bullet-proof code but it shows how easy it is to use the API.
I’m not going to pretend that I’m a data visualisation expert and I know these examples are very basic; however, I think there are a lot of possibilities here for someone with better data visualisation skills than me.
Now for the bad news: the Google Image Charts API has been deprecated since 2012! Here’s the statement on the Google website:
While the dynamic and interactive Google Charts are actively maintained, we officially deprecated the static Google Image Charts way back in 2012. This gives us the right to turn it off without notice, although we have no plans to do so.
Also, there’s a fair usage policy too:
There’s no limit to the number of calls per day you can make to the Google Chart API. However, we reserve the right to block any use that we regard as abusive.
As a result I would not be confident about using it in production. If thousands of Power BI users started using the API it might prompt Google to block traffic from Power BI or turn off the API completely!
I do think Microsoft really needs to address the lack of native support for sparklines and small multiples in Power BI – the fact we still don’t have them is frankly embarrassing (even Power View had them, for crying out loud). Although one solution could be a DAX function that returned a chart image – basically taking David’s work and wrapping it up in a more user-friendly form – another approach would be for Microsoft to build on the Report Page Tooltips functionality. Since we can already design mini reports and make them appear as tooltips, why not make it possible for the same mini reports to appear in a cell in a table or matrix? You could then have measures that returned the name of a report page as a text value, and a new data category for them that tells Power BI to display the contents of the report page in the cell instead of the text. That way you could create small multiples from any visual or set of visuals.
UPDATE: thanks also to Tom Martens for reminding me to point out that this technique involves sending data to a third party, something which might cause legal problems for you.