问题
I have a data frame with the following structure:
> t <- read.csv("combinedData.csv")[,1:7]
> str(t)
'data.frame': 699 obs. of 7 variables:
$ Awns : int 0 0 0 0 0 0 0 0 1 0 ...
$ Funnel : Factor w/ 213 levels "MEL001","MEL002",..: 1 1 2 2 2 3 4 4 4 4 ...
$ Plant : int 1 2 1 3 8 1 1 2 3 5 ...
$ Line : Factor w/ 8 levels "a","b","c","cA",..: 2 2 1 1 1 3 1 1 1 1 ...
$ X : int 1 2 3 4 7 8 9 10 11 12 ...
$ ID : Factor w/ 699 levels "MEL_001-1b","MEL_001-2b",..: 1 2 3 4 5 6 7 8 9 10 ...
$ BobWhite_c10082_241: int 2 2 2 2 2 2 0 2 2 0 ...
I want to construct a mixed effect model. I know in my data frame that the random effect I want to include (Funnel) is a factor, but it does not work:
> lmer(t$Awns ~ (1|t$Funnel) + t$BobWhite_c10082_241)
Error: couldn't evaluate grouping factor t$Funnel within model frame: try adding grouping factor to data frame explicitly if possible
In fact this happens whatever I want to include as a random effect e.g. Plant:
> lmer(t$Awns ~ (1|t$Plant) + t$BobWhite_c10082_241)
Error: couldn't evaluate grouping factor t$Plant within model frame: try adding grouping factor to data frame explicitly if possible
Why is R giving me this error? The only other answer I could google fu is that the random effect fed in wasn't a factor in the DF. But as str shows, df$Funnel certainly is.
回答1:
It is actually not so easy to provide a convenient syntax for modeling functions and at the same time have a robust implementation. Most package authors assume that you use the data parameter and even then scoping issues can occur. Thus, strange things can happen if you specify variables with DF$col syntax since package authors rarely spend a lot of effort to make this work correctly and don't include a lot of unit tests for this.
It is therefore strongly recommended to use the data parameter if the model function offers a formula method. Strange things can happen if you don't follow that praxis (also with other model functions like lm).
In your example:
lmer(Awns ~ (1|Funnel) + BobWhite_c10082_241, data = t)
This not only works, but is also more convenient to write.
来源：https://stackoverflow.com/questions/36650695/grouping-error-with-lmer