Summarize() vs. Summarize_at() in Corona Cases

Hi all,

In the corona cases cumulative project for the working with data section of the R course and I had a question about the summarize() vs. summarize_at() functions. My code ended up being off for a few reasons, but the main one I was confused on is the function you need to include. In the summarize() function, it seems you need to include the “()” after sum(), e.g. summarize(placeholder = sum()). In summarize_at(), however, my code wouldn’t run until I took the () off of sum(), e.g. summarize_at(vars(xyz), sum). Does anyone have insight into why that is? Frustrating because one would think the functions would require the same syntax.