12.9 Be careful about the numeric type

1. Often “numeric” is treated as synonymous for double:

# create a double and integeger objects
one <- 1
oneL <- 1L
typeof(one)
#> [1] "double"
typeof(oneL)
#> [1] "integer"

# check their type after as.numeric()
one |> as.numeric() |> typeof()
#> [1] "double"
oneL |> as.numeric() |> typeof()
#> [1] "double"

2. In S3 and S4, “numeric” is taken as either integer or double, when choosing methods:

sloop::s3_class(1)
#> [1] "double"  "numeric"
sloop::s3_class(1L)
#> [1] "integer" "numeric"

3. is.numeric() tests whether an object behaves like a number

typeof(factor("x"))
#> [1] "integer"
is.numeric(factor("x"))
#> [1] FALSE

But Advanced R consistently uses numeric to mean integer or double type.