Drill downs are extremely powerful. They can turn a simple bar chart into something that has potential for exploration. They are very effective in that they allow the user to explore the data further, whilst also saving space on the dashboard by effectively combining two bar charts into one.
Let's look at an example. Say we want to allow the user to see a basic bar chart of Sales by Category (as shown below), but when they click on a bar, they can uncover Sales by Sub Category.
Our first step is to create a Category parameter, by right clicking on Category in the Data pane, and allowing all values within the parameter.
In order to perform the drill down, we will need to create a calculation, instructing how we want the parameter to work.
The above calculation effectively tells us to return the Sub Category, if the corresponding Category matches our parameter, otherwise return nothing.
When we add our calculation to Rows, next to Category, we get the following view.
Currently, our view shows the Sales only within the Furniture category, as that is what is selected in our Parameter. In order to make our sheet dynamic, and responsive to the end user simply clicking one of the bars, we must add a parameter action.
The set up is very important. We must specify the correct sheet, parameter, and Source Field (in this case, we choose Category).
Similarly, we must ensure the selection is ran when the user Select's a bar, and specify that clearing the selection will Set Value to 'blank'. Setting the value to blank ensures that the drill down disappears when we click off the bar.
And there we have it, drill down bar charts are set for take off!
Note: When including a drill down option within a dashboard be sure to add instructions such that the end user knows how to interact with the chart.