R:使用as.formula修复模型调用

Question

我有一个gls模型，在该模型中，我为模型分配了一个公式(来自另一个对象)：

equation <- as.formula(aic.obj[row,'model'])
> equation
temp.avg ~ I(year - 1950)
mod1 <- gls(equation, data = dat)

> mod1
Generalized least squares fit by maximum likelihood
  Model: equation 
  Data: dat 
  Log-likelihood: -2109.276

，但是，，我不希望“模型”成为“等式”，而希望它本身就是“方程”！我该怎么做？？

Answer 1

这是非常标准的，就连lm也会这么做。一种方法:劫持print.gls函数

library('nlme')

(form <- follicles ~ sin(2*pi*Time) + cos(2*pi*Time))
# follicles ~ sin(2 * pi * Time) + cos(2 * pi * Time)

(fm1 <- gls(form, Ovary))

# Generalized least squares fit by REML
#   Model: form
#   Data: Ovary 
#   Log-restricted-likelihood: -898.434
# 
# Coefficients:
#   (Intercept) sin(2 * pi * Time) cos(2 * pi * Time) 
#    12.2155822         -3.3396116         -0.8697358 
# 
# Degrees of freedom: 308 total; 305 residual
# Residual standard error: 4.486121 

print.gls <- function(x, ...) {
  x$call$model <- get(as.character(x$call$model))
  nlme:::print.gls(x, ...)
}

fm1

# Generalized least squares fit by REML
#   Model: follicles ~ sin(2 * pi * Time) + cos(2 * pi * Time) 
#   Data: Ovary 
#   Log-restricted-likelihood: -898.434
# 
# Coefficients:
#   (Intercept) sin(2 * pi * Time) cos(2 * pi * Time) 
#    12.2155822         -3.3396116         -0.8697358 
# 
# Degrees of freedom: 308 total; 305 residual
# Residual standard error: 4.486121 

Answer 2

你可以用一些巧妙的语言破坏来解决这个问题。这将使用直接插入的模型方程创建(未评估的) gls调用，然后计算它。

cl <- substitute(gls(.equation, data=dat), list(.equation=equation))
mod1 <- eval(cl)