What is a context filter in Tableau?

A context filter in Tableau is a filter that improves performance by allowing processed data to be reduced before applying additional filters. When a context filter is set, Tableau first processes this filter and uses the subset of data it defines as the context for any subsequent filters applied. This means that only the data that meets the criteria of the context filter is considered, leading to better performance because Tableau can focus on a smaller set of data.

Using a context filter can significantly speed up the filtering process, especially when dealing with large datasets, as it narrows down the data Tableau needs to evaluate. This can be particularly useful in scenarios where you have multiple filters and want to optimize the analysis by first isolating relevant data for more efficient processing.

The other options describe different functionalities that do not accurately capture what a context filter does. For instance, a filter that categorizes different types of data does not inherently limit the dataset like a context filter does, and combining multiple datasets refers to joins or unions rather than filtering. Regarding the application timing of filters, a context filter is not applied after all other filters; rather, it is processed first, creating a foundation for subsequent filters.