[R] Error 0ps.factor: level sets of factors are different

I have two data sets: "new" and "combo". Within both data set, each row pertains to a unique individual. The "combo" data set is a subset of the "new" data set, meaning that all individuals within "combo" are within "new" but not all individuals within "new" are within "combo". Thus, nrow(new) > nr

[R] "argument is missing, with no default" OR "replacement has length zero"

Hello, I have a new data set and an old data set. Both have the same columns representing the same sort of measure. Within each data set (old and new) are 18 groups (simplified to three groups below). Within each group are individuals with unique ID numbers. These ID numbers may be the same as ot