[R] converting numeric to integer
Thomas Mang
thomas.mang at fiwi.at
Sat May 16 20:49:40 CEST 2009
Hello,
Suppose I have x, which is a variable of class numeric. The calculations
performed to yield x imply that mathematically it should be an integer ,
but due to round-off errors, it might not be (and so in either
direction). The error is however small, so round(x) will yield the
appropriate integer value. Moreover, this integer values is guaranteed
to be representable by an 'integer' class, that is -2^31 < x < 2^31, and
logically it is an integer anyway. So I want to convert x from class
'numeric' to 'integer'. What is the most elegant, but always correct
way, to achieve this conversion ?
What comes to mind is of course something along:
x = as.integer(round(x))
I am, however, not sure if this always works, because I do not know if
the round-function is guaranteed to return a numeric value which, in
finite binary representation, is always >= the underlying mathematical
integer. If that is however guaranteed, that would of course be a simple
+ elegant one.
An alternative I came up with is:
x = as.integer(round(x) + ifelse(x >= 0, 0.5, -0.5))
Where I explicitly add a bit to ensure the finite binary representation
must be >= the underlying integer, and then truncate the decimal digits.
IMO, this one is always guaranteed to work, at least within the
numerical range of what integers are limited to anyway.
What's your opinion on the issue ?
Any other solution ?
Thanks a lot in advance and cheers,
Thomas
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