重新聚合数据帧

Question

If our marriage data frame looks like this

   Month  Year marriage_counts
1    Jan  2011              50
2    Jan  2011              30
3    Jan  2011              20
4    Feb  2011              80
5    Feb  2011              10

and our Business data looks like this

  Month Year
1   Jan 2011
2   Jan 2011
3   Jan 2011
4   Feb 2011
5   Feb 2011

this should return a data frame that looks like

 Month Year marriage_count
1  Jan 2011            100
2  Feb 2011             90

but I'm stuck in here.. can anybody please help me?

Answer 1

In base R:

agg <- aggregate(marriage_counts ~ Month + Year, marriage, sum)

Via Dplyr:

library(dplyr)
df_marriage %>% group_by(Month, Year) %>% 
  summarise(marriage_count = sum(marriage_counts))

Via Data.table:

data.table::setDT(marriage)[, .(marriage_count = sum(marriage_counts)) , by = .(Month, Year)]

Answer 2

Another alternative using {purrr} . slice_rows() is equivalent to dplyr's group_by() .

library(purrr)
df_marriage <- data.frame(Month           = c("Jan", "Jan", "Jan", "May", "May"), 
                          Year            = 2011,
                          marriage_counts = c(50, 30, 20, 80, 10))

df_marriage %>% slice_rows(c("Month", "Year")) %>% by_slice(map, sum)