相关疑难解决方法(0)

我知道我们可以在通过引用创建列时动态添加列名称（使用:=），如下所述：Data.table 中的动态列名称。

但是，我希望在聚合时动态添加列名称。你能帮忙吗？

test_dtb <- data.table(a = sample(1:100, 100), b = sample(1:100, 100), id = rep(1:10, 10))
m = "blah"
test_dtb[ , list((m) = mean(b)), by = id]

我得到的错误是

Error: unexpected '=' in "test_dtb[ , list((m) =

假设我想创建一个从R中的data.table计算摘要数据集的函数,我希望能够以编程方式传递新计算变量的名称.

例如:

library(data.table)

# generate some fake data
set.seed(919)
dt <- data.table(x = rnorm(50), by.var = rep(c("a", "b"), 25))
dt[, list(group.means = mean(x)), by = "by.var"]  # This is what I want

# But I want to do in a function, so I can do it repeatedly:
groupMeans <- function(out.var, by.var, dat = dt) {
  return(dat[, list(out.var = mean(x)), by = by.var])  # doesn't work
}

groupMeans("group.means", "by.var")  # out.var should be "group.means"

我该怎么做呢？