Is There A Neat/Simplest Way To This data.table R Code?

The STRATUM from OECD data is so long, for simplicity I put this name and would like to simplified it to a more short and precise naming as in the code below.

pisaMas[,`:=`
             (SchoolType = c(ifelse(STRATUM == "National Secondary School", "Public", 
                                    ifelse(STRATUM == "Religious School", "Religious", 
                                           ifelse(STRATUM == "MOE Technical School", "Technical",0)))))]
pisaMas[,table(SchoolType)]

I would like to know if there are a simple way to this problems, using data.table package.