Picture the scene: you've built a dashboard with some lovely interaction controlled by parameter and / or set actions. You open the dashboard and select a mark to trigger an action.... And everything goes grey.
Okay maybe not everything.
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Above is an example of proportional brushing. When a segment is selected on the top chart, the proportion of the sub-category in the lower chart is shaded accordingly - this can be done with set or parameter actions.
Tableau automatically greys out the segments in the top chart which are not selected. While this has its use cases - its not what I want in this case. I want all my segments to be displayed in pink.
To rectify this we need to add a dummy highlight.
First, create a calculated field. Name it dummy and give it any string value (pro tip, you can zoom into you calculations by holding ctrl and scrolling):
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Second, add the dummy to the detail card of every chart on the dashboard.
Finally, open your dashboard. Select Dashboard > Actions from the toolbar. Create a new highlight action. Your source sheet needs to be the relevant dashboard and under 'Target Highlighting', select Selected Fields and choose your dummy field.
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Now you can select to your heart's content without losing any detail.