[R] Why is.integer() doesn't work with single values?

[Prof Brian D Ripley]

On Wed, 29 May 2002, Sven Garbade wrote:

> Hi all,
>
> I don't understand the behavior of is.integer():
>
> > x <- integer()
> > is.integer(x)
> [1] TRUE
> > x <- 10
> > is.integer(x)
> [1] FALSE
> > x <- 1:10
> > is.integer(x)
> [1] TRUE
>
> Why is.interger() returns FALSE if x has only one element? And how can
> someone check if x is an integer but contains only one value? (R 1.5.0
> on Linux i386)

Your guesses are wrong:

> is.integer(as.integer(10))
[1] TRUE
> is.integer(as.numeric(1:10))
[1] FALSE

If all else (except posting to R-help) fails, read the documentation which
says

     `is.integer' returns `TRUE' or `FALSE' depending on whether its
     argument is of integer type or not.

Note *NOT* `is an integer'.

To test for an integer *value* you could use x == round(x), assuming that
you want false for a value that is not integer by rounding error.
Otherwise use all.equal.

-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272860 (secr)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595

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