对公式使用非标准评估 [英] using non-standard evaluation with formula

问题描述

我正在创建使用非标准的软件包评估以跟踪列的含义.程序包在函数之间传递数据帧，这些函数执行各种操作来处理同一组列.非标准评估对此非常有用:

I'm creating a package that uses non-standard evaluation to keep track of the meaning of columns. The package passes a data frame among functions, which do various things do the same set of columns. Nonstandard evaluation works great for this:

my_select <- function(df, xcol, ycol) {
    new_df <- dplyr::select(df, !!xcol, !!ycol)
    new_df
}
my_select(mtcars, quo(wt), quo(mpg))

但是，我想要一个可与公式一起使用的函数:

However, I'd like a function that works with a formula:

my_lm <- function(df, xcol, ycol) {
    new_lm <- lm(!!xcol, !!ycol, data=df)
    new_lm
}
my_lm(mtcars, quo(wt), quo(mpg)

返回Error in !xcol : invalid argument type.我已经尝试过quo()，enquo()和!!的各种组合，但是基本的问题是我不知道lm需要什么样的对象.

returns Error in !xcol : invalid argument type. I've tried all sorts of combinations of quo(), enquo(), and !!, but the basic problem is that I don't know what kind of object lm needs.

推荐答案

您可以通过将公式的值粘贴在一起来创建公式，然后将该公式传递给lm.我敢肯定有更好的方法可以做到这一点，但这是一种可行的方法:

You can create a formula by pasting the values of the equation together, then pass the formula to lm. I'm sure there's a better way to do this, but here's one working approach:

library(rlang)

my_lm <- function(df, xcol, ycol) {
  form <- as.formula(paste(ycol, " ~ ", xcol)[2])
  my_lm <- lm(form, data=df)
  my_lm
}

my_lm(mtcars, quo(wt), quo(mpg))
#> 
#> Call:
#> lm(formula = form, data = mtcars)
#> 
#> Coefficients:
#> (Intercept)           wt  
#>      37.285       -5.344

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