在函数中粘贴公式（c 常数？）

Question

我正在做一个粘贴公式然后返回feols 结果的函数。但是，一开始我得到了一个c。我该如何解决这个问题？

library(dplyr)
library(fixest)

data(base_did)
base_did = base_did %>% mutate(D = 5*rnorm(1080),
                               x2 = 10*rnorm(1080),
                               rand_wei = abs(rnorm(1080)))

f <- function(data, arg=NULL){
  
  arg = enexpr(arg)
  
  if (length(arg) == 0) {
    formula = "D ~ 1"
  } 
  else {
    formula = paste(arg, collapse = " + ")
    formula = paste("D ~ ", formula, sep = "")
  }
  
  formula = paste(formula, " | id + period", sep = "")
  denom.lm <- feols(as.formula(formula), data = data, 
                    weights = abs(data$rand_wei))
  
  return(denom.lm)
}

f(base_did, arg = c(x1,x2))

#Error in feols(as.formula(formula), data = data, weights = abs(data$rand_wei)) : 
#  Evaluation of the right-hand-side of the formula raises an error: 
#  In NULL: Evaluation of .Primitive("c") returns an object of length 1
#while the data set has 1080 rows.

如果我最后return(formula)。我得到[1] "D ~ c + x1 + x2 | id + period"。

但我只需要D ~ x1 + x2 | id + period。

Answer 1

也许使您的函数工作的一种选择是通过... 传递参数，这样就不需要c，这会阻止c 添加到您的公式中。要完成这项工作，您还可以在函数内切换到 enexprs。

注意：我稍微调整了您的 reprex 函数以仅返回公式。

library(dplyr, warn = FALSE)
library(fixest)

data(base_did)

base_did = base_did %>% mutate(D = 5*rnorm(1080),
                               x2 = 10*rnorm(1080),
                               rand_wei = abs(rnorm(1080)))

f <- function(data, ...){
  arg = enexprs(...)
  
  if (length(arg) == 0) {
    formula = "D ~ 1"
  } 
  else {
    formula = paste(arg, collapse = " + ")
    formula = paste("D ~ ", formula, sep = "")
  }
  
  formula = paste(formula, " | id + period", sep = "")
  
  as.formula(formula)
}


f(base_did, x1, x2)
#> D ~ x1 + x2 | id + period
#> <environment: 0x7fe8f3567618>

f(base_did)
#> D ~ 1 | id + period
#> <environment: 0x7fe8f366f848>

更新可能有更好的方法，但经过一些研究，可能的选择是：

注意：当通过c 传递多个参数时，enexpr 将返回一个call 对象，该对象的行为类似于列表，其中第一个元素包含函数名称，即c。这就是为什么您将c 添加到您的公式中的原因。

f <- function(data, arg = NULL) {
  arg <- enexpr(arg)
  
  if (length(arg) == 0) {
    formula <- "D ~ 1"
  } else {
    if (length(arg) > 1) arg <- vapply(as.list(arg[-1]), rlang::as_string, FUN.VALUE = character(1))
    
    formula <- paste(arg, collapse = " + ")
    formula <- paste("D ~ ", formula, sep = "")
  }

  formula <- paste(formula, " | id + period", sep = "")

  as.formula(formula)
}


f(base_did, c(x1, x2))
#> D ~ x1 + x2 | id + period
#> <environment: 0x7fa763431388>

f(base_did, x1)
#> D ~ x1 | id + period
#> <environment: 0x7fa763538c40>

f(base_did)
#> D ~ 1 | id + period
#> <environment: 0x7fa765e22028>

Answer 2

如果您使用fixest 的内置公式操作工具（请参阅here），您可以极大地简化您的函数。特别是点方括号运算符：

library(fixest)
data(base_did)
n = 1080
base = within(base_did, {
    D = 5 * rnorm(n)
    x2 = 10 *rnorm(n)
    rand_wei = abs(rnorm(n))
    })

f = function(data, ctrl = "1"){
    feols(D ~ .[ctrl] | id + period,
          data = data, weights = ~abs(rand_wei))
}

est1 = f(base)
est2 = f(base, ~x1)           # with a formula
est3 = f(base, c("x1", "x2")) # with a character vector

etable(est1, est2, est3)
#>                     est1            est2             est3
#> Dependent Var.:        D               D                D
#>                                                          
#> x1                       0.0816 (0.0619)  0.0791 (0.0618)
#> x2                                       -0.0157 (0.0186)
#> Fixed-Effects:  -------- --------------- ----------------
#> id                   Yes             Yes              Yes
#> period               Yes             Yes              Yes
#> _______________ ________ _______________ ________________
#> S.E. type             --          by: id           by: id
#> Observations       1,080           1,080            1,080
#> R2               0.12810         0.13005          0.13094
#> Within R2             --         0.00224          0.00326
#> ---
#> Signif. codes: 0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1