Using dplyr to summarize by multiple groups

Question

I\'m trying to use dplyr to summarize a dataset based on 2 groups: \"year\" and \"area\". This is how the dataset looks like:

  Year   Area Num
1 2000 Area 1  99         


        

Answer 1

We can use data.table

library(data.table)
setDT(df)[, .(avg = mean(Num)) , by = .(Year, Area)]

Answer 2

Is this what you are looking for?

 library(dplyr)
 df <- group_by(df, Year, Area)
 df <- summarise(df, avg = mean(Num))