How to group by two columns in R

Question

I have a data frame that I am trying to group and then sum based on two columns. The two columns are characters with one being month and the other variable.

The foll

Answer 1

You apparently are not interested in taking your Character [month] as a Date variable. Considering that I'm not wrong you could simply do something like this:

library(dplyr)

tab %>%
  group_by(month, variable) %>%
  summarise(a_sum=sum(amount),
            a_mean=(mean(amount)))

and get this:

Source: local data frame [3 x 4]
Groups: month

  month variable a_sum a_mean
1 1-Jan        x  4000   2000
2 2-Feb        y  3000   3000
3 2-Feb        z  5000   5000