如何将变量粘贴到公式中

Question

当我尝试将变量粘贴到公式中时，我会遇到一个特殊的错误。我有以下变量：

# Choose explanatory variables 
vars_int <- c("age", 
              "male", 
              "race_ethnicity", 
              "patient_regional_location", 
              "marital_status", 
              "total_admits", 
              "chf", 
              "copd", 
              "diabwc", 
              "mld", 
              "cevd",
              "Obesity", 
              "Smoking")

当我将它们直接复制到公式中时，一切都很好：

# Generate inverse probability weights 
wts_17 <-  ipwpoint(
  exposure = exposure,
  family = "binomial",  
  link = "logit",
  denominator = ~ 
    age + 
    male + 
    race_ethnicity + 
    patient_regional_location + 
    marital_status + 
    total_admits + 
    chf + 
    copd + 
    diabwc + 
    mld + 
    cevd + 
    Obesity +
    Smoking,   
  data = df_17)

但是，当我尝试使用过去的功能进行操作时，一切都会崩溃：

paste("~", paste(vars_int, collapse = " + "))
[1] "~ age + male + race_ethnicity + patient_regional_location + marital_status + total_admits + chf + copd + diabwc + mld + cevd + Obesity + Smoking"

> wts_17 <-  ipwpoint(
+   exposure = exposure,
+   family = "binomial",  
+   link = "logit",
+   denominator = paste("~", paste(vars_int, collapse = " + ")),  
+   data = df_17)
Error in ipwpoint(exposure = exposure, family = "binomial", link = "logit",  : 
  Invalid denominator formula specified

有人知道为什么会发生这种情况吗？