Back to the table part of the question, but using Duncan's example.
> x <- c(3.4, 3.4 + 1e-15)
> unique(x)
[1] 3.4 3.4
> table(x)
x
3.4
2
The question was, why are these different.
table() only works on factors, so it converts the numeric vector to a
factor before tabulation.
factor() tries to do something sensible, and implicitly rounds the numeric data.
> factor(x)
[1] 3.4 3.4
Levels: 3.4
Whether you think that is actually sensible or not is up to you, but
if it isn't then you shouldn't use table.
That table uses factors is documented in ?table. A quick read of
?factor didn't find any explicit discussion, other than the
acknowledgement that factor() is lossy in:
To transform a factor ‘f’ to approximately its
original numeric values, ‘as.numeric(levels(f))[f]’ is recommended
and slightly more efficient than ‘as.numeric(as.character(f))’.
You can't even get table() to do what you want by being explicit:
> table(factor(x, levels = unique(x)))
Error in `levels<-`(`*tmp*`, value = as.character(levels)) :
factor level [2] is duplicated
Sarah
On Tue, Dec 10, 2019 at 9:18 AM Alain Guillet
<alain.guil...@uclouvain.be> 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?
>
>
> Best regards,
> Alain Guillet
>
--
Sarah Goslee (she/her)
http://www.numberwright.com
______________________________________________
R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
