difference in R between identical(x, y) and isTRUE(all.equal(x, y))

Question

suddenly a doubt...

is there any difference between testing isTRUE(all.equal(x, y)) and identical(x, y)?

the help page says:

Don't use 'all.equal' directly in 'if' expressions-either use 'isTRUE(all.equal(....))' or 'identical' if appropriate.

but that "if appropriate" leaves me in doubt. how do I decide which of the two is appropriate?

Answer 1

all.equal tests for near equality, while identical is more exact (e.g. it has no tolerance for differences, and it compares storage type). From ?identical:

The function ‘all.equal’ is also sometimes used to test equality this way, but was intended for something different: it allows for small differences in numeric results.

And one reason you would wrap all.equal in isTRUE is because all.equal will report differences rather than simply return FALSE.

Answer 2

identical is fussier. For example:

> identical(as.double(8), as.integer(8))
[1] FALSE
> all.equal(as.double(8), as.integer(8))
[1] TRUE
> as.double(8) == as.integer(8)
[1] TRUE