Aggregate Price Information From Two Different Slices with createSelector

In this lesson we take data from two different slices and combine the output in a single selector function. Because selectors get access to the entire RootState it's not hard to create these combinations. The other thing that's interesting here is that we're passing multiple input selectors into createSelector. You can read more about how that works below.

createSelector was brought in to RTK from the popular reselect library. While it's not needed to create selector functions, it makes it a lot easier to create efficient selectors that avoid doing more work than needed.

createSelector takes two types of arguments. There are inputSelectors (and there can be more than one of these) and then there's the resultFunction. You pass in these input selectors and then the result function processes the data that gets returned. As long as the input values don't change, the generated selector won't re-run the result function.

If the data you're working with isn't large or the calculations aren't complex, you don't really need to use createSelector. But it's a good tool to have in your toolbox.

Check out this link for more info: https://github.com/reduxjs/reselect#createselectorinputselectors--inputselectors-resultfunc