[R] How to get R to ignore certain values when analyzing a column in a data table ?

[Prof Brian Ripley]

On Sun, 9 Jul 2006, Daryl Manning wrote:

> Apologies if this is in (one of the many) manuals somewhere... Trying
> to switch to R from other stats programs.
>
> Basically, I have a large data table I've dumped from a DB, some of
> the values which are nulls '-' which I've converted to zeros. I've
> read it in using read.table fine.
>
> I want R to ignore the zero values when graphing or doing various
> other calculations.
>
> Is there a way to do this ?
>
> I did try to use NA but kept getting errors that x must be numeric.

Did you use numeric NA?  That is the way to so this, so you will need to 
give a reproducible example (as the posting guide asks).

-- 
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 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595