如何在 R dataframe 中聚合数据

Question

I have a dataframe that looks like

Col A | Col B | Col C
  1       2       3
  2       4       5
  3       1       3
  4       2       3

and I want to mutate my dataframe to aggregate Col B and Col C based on groups in col A. The col A groups are <= 2 and >2.

Col A | Col B | Col C
 <=2      6      8
  >2      3      6

How would I go about doing this?

Answer 1

You can try aggregate + ifelse like below

aggregate(
  . ~ ColA,
  transform(
    df,
    ColA = ifelse(ColA <= 2, "<=2", ">2")
  ), sum
)

which gives

  ColA ColB ColC
1  <=2    6    8
2   >2    3    6

---

A data.table option

> setDT(df)[, lapply(.SD, sum), .(ColA = ifelse(ColA <= 2, "<=2", ">2"))]
   ColA ColB ColC
1:  <=2    6    8
2:   >2    3    6