r - How do I increase or decrease an ordered factor's level? (Make a factor equal to the very next level) -

i have 2 lists of ordered factors , b, both contain thousands of items , have same ordinal scale of 30 levels. want find out how many items in equal or within 1 level above or below item @ same location in b

if scale numeric convert ordered factors numeric values , following:

table(a==b || a==(b+1) || a==(b-1)) 

however, of course, '+' not meaningful factors. do? write giant nested if statement or change ordinal scale numbers according level can convert ordered factors numeric... these seem roundabout (and lengthy) solutions i'd assume easy: how increase or decrease ordered factor's level?

if have

x<-ordered("b",levels=c("a","b","c")) 

how make x[1] equal "c" incrementing current level?

sidenote: of course, in first example above i'd need account factors on lower , upper end of scale, think (hope) easy enough figure out once question has been answered.

you should able modify example output want

set.seed(7) df <- data.frame(a=sample(paste('a',seq(1:5),sep=''),5000,replace=true),                  b=sample(paste('a',seq(1:5),sep=''),5000,replace=true)) table(df$a) table(df$b) fa=factor(levels(df$a))  ia=0 (a in fa) {   ia=ia+1   cat('for factor',a,'\n')   na = sum(df$a==a)   nb = sum(df$b==a)   cat('  df$a has',na,'\n')   cat('  df$b has',nb,'\n')   nbm1 = -1   if (ia>1) {     am1 <- fa[ia-1]     nbm1 = sum(df$b==am1)     cat('  df$b has',as.character(am1),', ',nbm1,'\n')   }   nbp1 = -1   if (ia<length(fa)) {     ap1 <- fa[ia+1]     nbp1 = sum(df$b==ap1)     cat('  df$b has',as.character(ap1),', ',nbp1,'\n')   }   if (na == nbm1) {     cat('    df$a[a] has same number df$b[a-1]\n')   } else {     cat('    df$a[a] not have same number df$b[a-1]\n')   }   if (na == nbp1) {     cat('    df$a[a] has same number df$b[a+1]\n')   } else {     cat('    df$a[a] not have same number df$b[a+1]\n')   } }