问题描述
我想用 nnet::multinom()
拟合多项式模型并用 ggeffects::ggemmeans()
进行预测。虽然这样的过程在常规代码中工作,但我未能将其包装在函数中。
示例
数据
library(dplyr)
my_mtcars <-
mtcars %>%
mutate(across(c(vs,carb),as.factor)) %>%
as_tibble()
拟合和预测的工作方式如下
library(nnet) # 7.3-15
library(emmeans) # 1.5.4
library(ggeffects) # 1.0.2
m <- multinom(carb ~ vs,data = my_mtcars)
ggemmeans(model = m,terms = "vs")
## # Predicted probabilities of carb
## # x = vs
## # Response Level = 1
## x | Predicted | 95% CI
## ----------------------------
## 0 | 0.00 | [0.00,0.00]
## 1 | 0.50 | [0.43,0.57]
## # Response Level = 2
## x | Predicted | 95% CI
## ----------------------------
## 0 | 0.28 | [0.24,0.32]
## 1 | 0.36 | [0.30,0.42]
## # Response Level = 3
## x | Predicted | 95% CI
## ----------------------------
## 0 | 0.17 | [0.14,0.19]
## 1 | 0.00 | [0.00,0.00]
## # Response Level = 4
## x | Predicted | 95% CI
## ----------------------------
## 0 | 0.44 | [0.39,0.50]
## 1 | 0.14 | [0.12,0.17]
## # Response Level = 6
## x | Predicted | 95% CI
## ----------------------------
## 0 | 0.06 | [0.05,0.06]
## 1 | 0.00 | [0.00,0.00]
## # Response Level = 8
## x | Predicted | 95% CI
## ----------------------------
## 0 | 0.06 | [0.05,0.00]
但是当我尝试将此过程包装在自定义函数中时它失败了
my_multinom <- function(dat,dv,expl) {
frmla <- as.formula(paste0(dv,"~",expl))
model_fit <- nnet::multinom(frmla,data = dat)
ggemmeans(model = model_fit,terms = expl)
}
my_multinom(dat = my_mtcars,dv = "carb",expl = "vs")
object$call$formula[[2]] 中的错误:
“符号”类型的对象不可子集
值得注意的是,问题似乎在于 multinom()
和 ggemmeans()
之间的交互。如果我们从 ggemmeans()
中省略 my_multinom()
那么它似乎可以正常工作:
my_multinom_no_ggemmeans <- function(dat,expl))
model_fit <- nnet::multinom(frmla,data = dat)
model_fit
}
my_multinom_no_ggemmeans(dat = my_mtcars,expl = "vs")
## # weights: 18 (10 variable)
## initial value 57.336303
## iter 10 value 38.192450
## iter 20 value 37.940409
## final value 37.940164
## converged
## Call:
## nnet::multinom(formula = frmla,data = dat)
## Coefficients:
## (Intercept) vs1
## 2 13.44961 -13.78607
## 3 12.93879 -33.99280
## 4 13.91961 -15.17237
## 6 11.84015 -23.96194
## 8 11.84015 -23.96194
## Residual Deviance: 75.88033
## AIC: 95.88033
知道为什么 my_multinom()
包装器失败吗?
更新
我可能已经找到了解决方案,但我不明白为什么它有效。基于 this github issue(不同的包),我调整了以下解决方案:
my_multinom_with_do.call <- function(dat,expl) {
frmla <- as.formula(paste0(dv,expl))
model_fit <- do.call(multinom,args = list(formula = frmla,data = dat))
ggemmeans(model = model_fit,terms = expl)
}
它有效:
my_multinom_with_do.call(dat = my_mtcars,expl = "vs")
但为什么这有效而我原来的 my_multinom()
没有?
解决方法
由于懒惰的评估,它不起作用。 call
的 model_fit
成员有 formula = frmla
,未计算。对该模型的 emmeans
支持需要一个公式。如果您在原始函数中添加一行,它将起作用:
my_multinom <- function(dat,dv,expl) {
frmla <- as.formula(paste0(dv,"~",expl))
model_fit <- nnet::multinom(frmla,data = dat)
model_fit$call$formula <- frmla
ggemmeans(model = model_fit,terms = expl)
}
do.call
方法有效的原因是 frmla
在您创建传递给 do.call
的列表时被评估。