如何将新摘要列的名称传递给函数中的data.table？

Question

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？

Answer 1

由docendo discimus提供,您可以使用创建的命名列表setNames,如下所示:

groupMeans <- function(out.var, by.var, dat = dt) {
  return(dat[, setNames(list(mean(x)), out.var), by = by.var])  
}

groupMeans("group.means", "by.var")
#    by.var group.means
# 1:      a  -0.1159832
# 2:      b   0.2910531