Remove some factor-interaction terms from estimation
问题 I'd like to remove certain factor interactions from an estimation. Here's an example with generated data from an imaginated labour market (I uploaded it here: http://pastebin.com/raw.php?i=EcMEVqUC) s <- source("http://pastebin.com/raw.php?i=EcMEVqUC")$value lm(income ~ age + cit * prof, data=s) In this example economy, foreigners are not allowed to work in the public sector, therefore citforeign:profofficial is NA . Therefore I would like to exclude the interaction term of citforeign