如何在R'中保留“backticks”；s quote（）即使不需要？

我知道一些字符，如

-

（连字符）或

（空格）不应该在常规的R名称中使用，因此我需要在特定场景中使用它们

下面是一个最小的可重复的例子来说明这个问题

给出下表

library(data.table)

dat <- data.table(x = 1:8, 
                  y = rep(rep(c("a", "b"), each = 2), 2), 
                  `y-z` = rep(c("c", "d"), each = 4))

现在考虑一下，我想在列表中或平原上指定一些查询（不要紧）。 当我检查

arg1

和

arg_列表[[“arg1”]]

或

arg_列表[[“arg4”]]

的输出时，我知道回跳已经消失。但显然，我需要它们在

data.table

的

by=

参数中构造适当的查询

---

有没有办法解决所有的问题？谢谢

最后你可以

eval

，这可能会更简单。比如说,

> ex = substitute(dat[, sum(x), by=myby], list(myby = quote(list(y, `y-z`))))
> eval(ex)
   y y-z V1
1: a   c  3
2: b   c  7
3: a   d 11
4: b   d 15

然后，您的问题是如何构建表达式

quote（list（y，`y-z`）

，这是一个基本的R问题，不需要详细了解

DT[，…，by=eval（…）]

在内部做什么

对于OP的对象，这里有一种方法，使用

调用
：

myby = with(arg_list, call("list", arg1, arg2))
ex = substitute(dat[, sum(x), by=myby], list(myby = myby) )
eval(ex)

从OP的注释中，您还可以在
call（…）
中命名参数：

如果有人在data.table中查找命名参数，只需使用一个不带引号的表达式
myby=with（arg_list，call（“list”，arg1，sub=arg3））
–忍者

谢谢，这个很有魅力！：）如果有人在
data.table
中查找命名参数，可以简单地使用一个不带引号的表达式
myby=with（arg_list，call（“list”，arg1，sub=arg3））
@ninjaminb Cool，很高兴它能工作：）我不知道重新命名的args——我已经将它添加到了答案中。
# simple cases
dat[, sum(x), by = eval(arg1, envir = .SD)] # works
dat[, sum(x), by = eval(arg2, envir = .SD)] # works
dat[, sum(x), by = eval(arg_list[["arg1"]], envir = .SD)] # works
dat[, sum(x), by = eval(arg_list[["arg2"]], envir = .SD)] # works

# complex cases in which "by" is constructed
dat[, sum(x), by = .(`y`, `y-z`)] # works
dat[, sum(x), by = eval("`y`, `y-z`", envir = .SD)] # works
dat[, sum(x), by = eval(paste(c("`y`,", "sub =", "`y-z`"), collapse = ""), envir = .SD)] # works
dat[, sum(x), by = eval(paste(c("`y`,", "sub =", arg2), collapse = ""), envir = .SD)]    # works
dat[, sum(x), by = eval(paste(c("`y`,", "sub =", "`y`"), collapse = ""), envir = .SD)]   # works
dat[, sum(x), by = eval(paste(c("`y`,", "sub =", arg1), collapse = ""), envir = .SD)]    # fails

dat[, sum(x), by = eval(paste(c("`y`,", "sub =", arg_list[["arg2"]]), collapse = ""), envir = .SD)] # works
dat[, sum(x), by = eval(paste(c("`y`,", "sub =", arg_list[["arg1"]]), collapse = ""), envir = .SD)] # fails

# probably even more complex cases
dat[, sum(x), by = eval(paste(c("`y`, sub = `y-z` == 'd'"), collapse = ""), envir = .SD)] # works
dat[, sum(x), by = eval(paste(c("`y`,", "sub =", arg_list[["arg4"]]), collapse = ""), envir = .SD)] # works
dat[, sum(x), by = eval(paste(c("`y`,", "sub =", arg_list[["arg3"]]), collapse = ""), envir = .SD)] # fails

> ex = substitute(dat[, sum(x), by=myby], list(myby = quote(list(y, `y-z`))))
> eval(ex)
   y y-z V1
1: a   c  3
2: b   c  7
3: a   d 11
4: b   d 15

myby = with(arg_list, call("list", arg1, arg2))
ex = substitute(dat[, sum(x), by=myby], list(myby = myby) )
eval(ex)