f=factor(c("A","A","B","B","C","D","E"))
print(table(f))
f1=delevels(f,"A","a")
print(table(f1))
f2=delevels(f,c("C","D","E"),"CDE")
print(table(f2))
f3=delevels(f,c("B","C","D","E"))
print(table(f3))
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