Sparklines (2)

Last September I wrote here about sparklines, their uses and the upcoming implementation in Excel 2010. By now I've had the chance to try out the sparkline functionality in the Office 2010 preview release and I'm pretty positive about the experience.

I downloaded a set of daily averaged exchange rate data for the last three months. This gives me a table with 279 data points (most are hidden in the example below for readability's sake), all of which are decimals with tiny variations. Not very readable, then, and certainly difficult to interpret without careful study. If I add three sparklines though, I have an instant, in-context overview of the general trends: it's clear that the Euro has taken a significant fall in value in the past three months.

The value of these small but intensely data-rich graphs should be clear (though if you're still not convinced I'd urge you to read Prof. Tufte's writings on the subject), but how does the Microsoft implementation stack up?

Firstly, it's extremely simple to use, more so than the regular Excel charting tools. The presentation options are necessarily much more limited, but there's a choice of three formats (line, as shown here, column, and win-loss) and lowest and highest points can be highlighted. I've done so in this example, with a green dot showing the minimum data point and a red dot indicating the maximum value. Resizing the sparkline cell resizes the graph automatically, and it's easy to change colours and the likes.

There are some minus points too, though. It appears to be impossible to combine sparklines in a cell, so you can't have lines from two different data sets overlaid on each other, or show (for instance) expected or normal values/value ranges together with the sparkline. I had expected that saving a sparklined workbook in Excel 97-2003 (.xls) format wouldn't preserve the sparkline, but I was surprised when I opened a sparklined workbook in Excel 2007. The .xlsx file format hasn't changed, so I figured that my sparklines might be saved as images, or displayed as miniature line charts, but instead the cells just showed up blank.

I'm not sure if this behaviour will also show up in the final release, but it would be a real shame if one couldn't share sparklined workbooks with Office 2007 users. That apart, it's a very creditable effort from Microsoft and a valuable addition to the Excel toolbox.