How can I compare two factors with different levels?

Question

Is it possible to compare two factors of same length, but different levels? For example, if we have these 2 factor variables:

A <- factor(1:5)

str(A)
 Factor w/ 5 levels "1","2","3","4",..: 1 2 3 4 5

B <- factor(c(1:3,6,6))

str(B)
 Factor w/ 4 levels "1","2","3","6": 1 2 3 4 4

If I try to compare them using, for example, the == operator:

mean(A == B)

I get the following error:

Error in Ops.factor(A, B) : level sets of factors are different

Answer 1

Convert to character then compare:

# data
A <- factor(1:5)
B <- factor(c(1:3,6,6))

str(A)
# Factor w/ 5 levels "1","2","3","4",..: 1 2 3 4 5
str(B)
# Factor w/ 4 levels "1","2","3","6": 1 2 3 4 4

mean(A == B)

Error in Ops.factor(A, B) : level sets of factors are different

mean(as.character(A) == as.character(B))
# [1] 0.6

Or another approach would be

mean(levels(A)[A] == levels(B)[B])

which is 2 times slower on a 1e8 dataset.