(Note: It's not very easy to find, but you can customize how the graphics on your page interact with each other. Click on one graphic to activate it; then on the Format ribbon, choose Edit Interactions. The other graphics on the page will all have some additional icons: A filter and a circle with slash through it. Clicking on the filter means that graphic will change based on what happens in the active graphic; clicking the circle with slash means it will not.)
It's also easy to take the same graphics and decide to look at medians instead of averages, since a few unlucky very late flights could have an outsized effect on overall averages. As in Excel, you can add a page to your Power BI report by clicking the plus sign next to the tab with the page name (default should be Page 1).
Even handier, since we've got slicers and a graph all set up: Right-click on the page and duplicate it. It's now pretty easy to click on the graph; under the Value section, click on Average of Dep Delay and Average of Arr Delay and change each to Median. If you're following along, you'll also want to change the title of the graph and the table with flight data from Average to Median.
Every airline had a 0 or below median arrival delay for all these cities combined -- except for Spirit. When I just look at flights arriving in Boston, Spirit's delays look even more pronounced -- although to be fair, they might have just had a bad summer in 2015 and improved since then.
A graph showing flights arriving in Boston.
Interested in how average delays break down by month? Power BI has automatic drilldown by date fields, which we can see by creating a new visualization on a new page.
Again, right-click on Page 1 and duplicate it, click on the graph to activate it, then unclick Airlines and click on FL_DATE. You'll only see two bars on the chart, one each for arrival and departure.
That's because Power BI defaults to graphing by year, and we've only got one year's worth of data. Under Axis, you can click the x next to Year to delete that so the graph will stop aggregating annually (which is somewhat useless for this data). It now defaults to Quarter. That, too, isn't much use for this particular four-month data set, but let's pretend it is.
To enable Power BI's date drilldown, click the down arrow at the top right of the graph. Now, if you click one of the third-quarter bars, it will drill down to show you months. Click a month's bar, and it will zoom in on days for that month.
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