Combining sapply() with group_by()

[jmcvw]

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1. Yes you can use any function you like in FUN
2. Doing it as you are, is using an "anonymous" function - you might find it easier to visualize if you pull the function out and create a standalone function.
3. Some functions (eg summary) are quite happy to work on a dataframe. Othere like 'mean / 'median etc will only work on a vector, so you can say for example mean(iris[1:4]).
   . To do what you are doing you would have to loop over each column, then loop over each function, while looping over each group of the data - doable but troublesome.
4. Think about what I said earlier: tidyverse it will work better with summarize
   • While the tidyverse functions will often play fine with base R, they are really designed to work with other tidyverse functions, and will perform far better doing so.