Now what I'm not going to do here is talk about Context Filters in terms of performance. My experience with using context filters to improve performance is very hit and miss, sometimes it works, sometimes it slows things down and sometimes there is no difference. This all depends on your data connection type, the size and width of your data and what you are trying to achieve with the filter. For improving performance with context filters I suggest you utilise the ever popular 'try it and see' approach. I am going to talk about Context Filters in terms of functionality and give some examples.
First up, how do I make a regular filter a Context Filter?
This one's easy - you simply right click on your filter pill (or click the drop down arrow) and select 'Add to Context'.
You will notice that the filter pill turns grey. This is, in classic subtle Tableau style, your clue that the filter is 'in context.
Also worth noting is that context filters can be for single sheets, multiple sheets or all sheets. But it will be in or out of context for all sheets, you can't apply to many sheets and then switch in and out of context on different sheets.
Aggregation based filters (e.g. sum(sales)) cannot be added to context.
What does a Context Filter actually do?
In simple terms, putting a filter in context ensures that all other filters are dependent on that Context Filter. Tableau filters otherwise act independently and this is a useful feature, but may sometimes mean that filtering doesn't do what you might first expect it to do.
