来自数据表d
例如
require(data.table)
d = data.table(a = 1:4, b = 11:14, c = 21:24, group = c(1,1,2,2))
我想对名称存储在向量中的所有变量求和varsToSum
通过独特的价值观group
.
varsToSum = c("a", "b")
对于以上情况d
and varsToSum
,预期结果是
d[,list(a = sum(a), b = sum(b)),list(group)]
group a b
1: 1 3 23
2: 2 7 27
相关文章:
d[, lapply(.SD, sum), by = group, .SDcols = varsToSum]
group a b
1: 1 3 23
2: 2 7 27
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