The question is below.

Researchers have set five proficiency levels in CIL: Below Level 1, Level 1, Level 2, Level 3, and Level 4. For simplicity, we recode them as two levels combining Level 3 and 4 as “Proficient” and all other lower levels (Level 2 and below) as “Developing”. Use PV1CIL and the cut score of 577 (577 included for “Proficient”) to create a new dependent variable of CIL_LEVEL (1 for “Proficient” and 0 for “Developing”). Please make sure if you create this new variable correctly by using aggregate with embedded range function.

The data name is CT_KOR.
I found there is no five CIL level variables in CT_KOR.
So, I assign “Developing”, and ” Proficient” to CIL_LEVEL.
I don’t know what to do after that.

CIL_LEVEL <- c("Developing", "Proficient")
Proficient <- CT_KOR$PV1CIL >= 577
Developing <- CT_KOR$PV1CIL < 577
aggregate(PV1CIL ~ CIL_LEVEL, data = CT_KOR, mean)

As expected, it doesn’t work, appearing an error message.
Please help me.