Dear John,
Printing inside the function is problematic. Your function itself does
NOT print the labels.
Just as a clarification:
F = factor(rep(1:2, 2))
by(data.frame(V = 1:4, F = F), F, function(x) { print(x); return(NULL); } )
#?? V F
# 1 1 1
# 3 3 1
#?? V F
# 2 2 2
# 4 4 2
# F: 1 <- this is NOT printed inside the function
# NULL
# ---------------------------------------------------------
# F: 2
# NULL
### Return Results
by(data.frame(V = 1:4, F = F), F, function(x) { return(x); } )
# F: 1
# ? V F
# 1 1 1
# 3 3 1
# --------------------------------------------------
# F: 2
#?? V F
# 2 2 2
# 4 4 2
Maybe others on the list can offer further assistance.
Sincerely,
Leonard