R: factor levels, recode rest to 'other'

Question

I use factors somewhat infrequently and generally find them comprehensible, but I often am fuzzy about the details for specific operations. Currently, I am coding/collapsing cat

Answer 1

I think the easiest way is to relabel all the naics not in the top 8 to a special value.

data$naics[!(data$naics %in% top8)] = -99

Then you can use the "exclude" option when turning it into a factor

factor(data$naics, exclude=-99)