ignoring zeros or converting to NA

The help page on binary operators (see ?"==") confirms that binary
representation of fractional representation is not catered for and
points to all.equal as a more suitable test method for those cases.

Steve E

Thomas Lumley <tlumley at u.washington.edu> 13/08/2008 16:47 >>>

Integers (up to a fairly high limit) are represented exactly, as are
fractions whose denominator is a power of two (again up to a fairly high
limit), so x==0 is fine in that sense.

If x is computed by floating point operations you do have to worry
whether these are exact, eg, with
   x<-seq(-1,1,length=7)
it is not clear that the fourth element will be exactly zero.

     -thomas

Hi,

since many suggestions are following the form of
x[x==0] (or similar)
I would like to ask if this is really recommended?
What I have learned (the hard way) is that one should not test for

equality of

floating point numbers (which is the default for R's numeric values,

right?)

since the binary representation of these (decimal) floating point

numbers is

not necessarily exact (with the classic example of decimal 0.1).
Is it okay in this case for the value zero where all binary elements

are zero?

Or does R somehow recognize that it is an integer?

Just some questions out of curiosity.

Thank you,
Roland


rcoder wrote:

Hi everyone,

I have a matrix that has a combination of zeros and NAs. When I

perform

certain calculations on the matrix, the zeros generate "Inf" values.

Is

there a way to either convert the zeros in the matrix to NAs, or

only

perform the calculations if not zero (i.e. like using something

similar to

an !all(is.na() construct)?

Thanks,

rcoder

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Thomas Lumley			Assoc. Professor, Biostatistics
tlumley at u.washington.edu	University of Washington, Seattle

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