But does it have a decimal?

doesithaveadecimal.R

has_decimal <- function(x){ (x - floor(x)) > 0 }

## from ?is.integer 
is.wholenumber <-
    function(x, tol = .Machine$double.eps^0.5)  abs(x - round(x)) < tol

## from http://stackoverflow.com/questions/3476782/how-to-check-if-the-number-is-integer/3477158#3477158

## from SO and also twitter https://twitter.com/polesasunder/status/700091075269005313
is_whole <- function(x) x%%1==0
## apparently this is rather fast