R，data.table：对名称存储在向量中的所有列求和

Question

来自data.table d 例如

require(data.table)
d = data.table(a = 1:4, b = 11:14, c = 21:24, group = c(1,1,2,2))

我想通过 group 的唯一值将名称存储在向量 varsToSum 中的所有变量相加。

varsToSum = c("a", "b")

对于上述d和varsToSum，预期的结果是

d[,list(a = sum(a), b = sum(b)),list(group)]

   group a  b
    1: 1 3 23
    2: 2 7 27

---

相关帖子：

• Select / assign to data.table variables which names are stored in a character vector

• How to go from a vector of strings to a vector of quotes / names?

Answer 1

d[, lapply(.SD, sum), by = group, .SDcols = varsToSum]

   group a  b
1:     1 3 23
2:     2 7 27