当“按”分组变量存储为字符串向量时总结data.table [重复]答案

【问题标题】：Summarise data.table when "by" grouping variables stored as vector of strings [duplicate]当“按”分组变量存储为字符串向量时总结data.table [重复]
【发布时间】：2020-06-26 19:19:54
【问题描述】：

我正在尝试将数据表总结为函数的一部分。分组变量根据用户要求/数据而变化。分组变量作为字符串向量输入。如何将其用作分组变量？见下面的代码

library(data.table)
test <- as.data.table(mtcars)

grouping_vars <- c("vs", "am")

#does what I would like
test[,.(counts = .N,
       mpg = mean(mpg),
       disp = median(disp)), by = .(vs,am)]

#throws error
test[,.(counts = .N,
       mpg = mean(mpg),
       disp = median(disp)), by = .(grouping_vars)]

#only gets the first variable
test[,.(counts = .N,
       mpg = mean(mpg),
       disp = median(disp)), by = .(get(grouping_vars))]

【问题讨论】：

标签： r data.table

【解决方案1】：

这里我们可以用c(代替.(

library(data.table)
test[,.(counts = .N,
    mpg = mean(mpg),
    disp = median(disp)), by = c(grouping_vars)]
#    vs am counts      mpg  disp
#1:  0  1      6 19.75000 160.0
#2:  1  1      7 28.37143  79.0
#3:  1  0      7 20.74286 167.6
#4:  0  0     12 15.05000 355.0

【讨论】：