The summarise example I gave creates a single new column (some_col), that is a function of two columns from the grouped data frame. Passing a map to agg is just

The summarise example I gave creates a single new column (some_col), that is a function of two columns from the grouped data frame. Passing a map to agg is just creating multiple columns, each a function of at most a single column in the dataframe. (I should have used a better example, like summarise(gdf, some_col = f(cola / colb))