在ggplot中绘制具有固定效应相互作用的混合效应模型

Question

我正在绘制基于 lmer() 对象的混合效应模型中固定效应的相互作用。为此，我根据我的模型预测新值。这工作正常，除了由于我生成它们的方式，预测延伸到整个可能的 x 轴范围。我现在可以通过基于循环定义 new.dat（根据分组变量 "Variety" 更改最大值和最小值）等，将预测的回归线限制在各自分组变量的范围内，但是 - 是有更优雅/更简单的解决方案来绘制这个吗？我是否错过了什么（我对 R 比较陌生）？

数据：

library(datasets)
data("Oats")

# manipulate data so it resembles more my actual data
Oats <- Oats %>%
  filter((Variety == "Golden Rain"  & nitro>=0.2) | (Variety == "Marvellous" & nitro <=0.4) | (Variety == "Victory" & nitro<=0.4 & nitro>=0.2))  #%>%

模型和绘图：

mod2 <- lmer(yield ~ nitro * Variety + (1| Variety), data=Oats)

new.dat <- data.frame(nitro=seq(min(Oats$nitro),max(Oats$nitro), length.out = 48), Variety= Oats$Variety)
new.dat$pred<-predict(mod2,newdata=new.dat,re.form=~0)

ggplot(data=Oats, aes(x=nitro, y=yield, col = Variety)) +
  geom_point() +
  geom_line(data=new.dat, aes(y=pred)) +
  geom_point(data=new.dat, aes(y=pred))

非常感谢您的每一个提示！

Answer 1

您可以通过计算每个组的 min/max 然后按组计算序列来获得它。继续使用 tidyverse，因为您的代码已经在使用它：

library(tidyverse)
library(pairwiseCI)
#> Loading required package: MCPAN
#> Loading required package: coin
#> Loading required package: survival
library(lme4)
#> Loading required package: Matrix
#> 
#> Attaching package: 'Matrix'
#> The following objects are masked from 'package:tidyr':
#> 
#>     expand, pack, unpack

data("Oats")

 ## manipulate data so it resembles more my actual data
Oats <-
  Oats %>%
  filter((Variety == "Golden Rain"  & nitro>=0.2) | (Variety == "Marvellous" & nitro <=0.4) | (Variety == "Victory" & nitro<=0.4 & nitro>=0.2))  #%>%

mod2 <- lmer(yield ~ nitro * Variety + (1| Variety), data=Oats)
#> Warning in checkConv(attr(opt, "derivs"), opt$par, ctrl = control$checkConv, :
#> unable to evaluate scaled gradient
#> Warning in checkConv(attr(opt, "derivs"), opt$par, ctrl = control$checkConv, :
#> Hessian is numerically singular: parameters are not uniquely determined

## Calculate min/max by group
all_vals <-
  Oats %>%
  group_by(Variety) %>%
  summarize(min_nitro = min(nitro),
            max_nitro = max(nitro))
## Calculate sequence for each group
new.dat <-
  all_vals %>%
  group_split(Variety) %>%
  map_dfr(~ data.frame(Variety = .x$Variety, nitro = seq(.x$min_nitro, .x$max_nitro, length.out = 20)))


new.dat$pred<-predict(mod2,newdata=new.dat,re.form=~0)

ggplot(data=Oats, aes(x=nitro, y=yield, col = Variety)) +
  geom_point() +
  geom_line(data=new.dat, aes(y=pred)) +
  geom_point(data=new.dat, aes(y=pred))

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