table and unique seems to behave differently

On 10/12/2019 3:53 a.m., Alain Guillet wrote:

Hi,

I have a vector (see below the dput) and I use unique on it to get

unique values. If I then sort the result of the vector obtained by
unique, I see some elements that look like identical. I suspect it
could be a matter of rounded values but table gives a different result:
unlike unique output which contains "3.4  3.4", table has only one cell
for 3.4.

Can anybody know why I get results that look like incoherent between

the two functions?

dput() does some rounding, so it doesn't necessarily reproduce values
exactly.  For example,

x <- c(3.4, 3.4 + 1e-15)
unique(x)
#> [1] 3.4 3.4
dput(x)
#> c(3.4, 3.4)
identical(x, c(3.4, 3.4))
#> [1] FALSE

If you really want to see exact values, you can use the "hexNumeric"
option to dput():

dput(x, control = "hexNumeric")
#> c(0x1.b333333333333p+1, 0x1.b333333333335p+1)
identical(x, c(0x1.b333333333333p+1, 0x1.b333333333335p+1))
#> [1] TRUE

Duncan Murdoch