Я думаю, что вам нужно противоположно тому, что вы пытались. Попробуйте:
aggregate(TUCASEID~., df, mean)
# AGE MALE BLACK YEAR DATASET INTERVIEW_DAY INTERVIEW_DATE TUCASEID
#1 60 1 1 2003 2003 5 03Jan2003 2e+13
#2 41 0 0 2003 2003 6 04Jan2003 2e+13
data
df <- structure(list(TUCASEID = c(2.00301e+13, 2.00301e+13, 2.00301e+13,
2.00301e+13, 2.00301e+13, 2.00301e+13, 2.00301e+13, 2.00301e+13,
2.00301e+13, 2.00301e+13), AGE = c(60L, 60L, 60L, 60L, 60L, 60L,
60L, 60L, 60L, 41L), MALE = c(1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L,
1L, 0L), BLACK = c(1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 0L), YEAR = c(2003L,
2003L, 2003L, 2003L, 2003L, 2003L, 2003L, 2003L, 2003L, 2003L
), DATASET = c(2003L, 2003L, 2003L, 2003L, 2003L, 2003L, 2003L,
2003L, 2003L, 2003L), INTERVIEW_DAY = c(5L, 5L, 5L, 5L, 5L, 5L,
5L, 5L, 5L, 6L), INTERVIEW_DATE = structure(c(1L, 1L, 1L, 1L,
1L, 1L, 1L, 1L, 1L, 2L), .Label = c("03Jan2003", "04Jan2003"), class =
"factor")), class = "data.frame", row.names = c("1",
"2", "3", "4", "5", "6", "7", "8", "9", "10"))