Thank you Ted and David for prompt reply.

I can accept Inf but can not use for plotting, which I intend to do.  May be
I can add 1/(10^308), so that if something comes to 0 will be in -log10
scale be 308.

Ram H

On Sun, Aug 28, 2011 at 12:12 PM, Ted Harding <ted.harding@wlandres.net>wrote:

> On 28-Aug-11 15:37:06, Ram H. Sharma wrote:
> > Dear R users:
> > Sorry for this simple question:
> >
> > I am writing a function where I would need to pickup p values
> > and make -log10 of it.
> >
> > The p values are from an anova output and sometime it can
> > yield me 0.
> >
> > -log10 (0)
> >
> > [1] Inf
> >
> > I can not replace Inf with 0, which not case here.
> >
> >
> > This is restricting me to go further in the function and out
> > me the error.
> > You help is highly appreciated.
> >
> > Thanks;
> > --
> > Ram H
>
> You cannot do anything about -log10(0) except to accept "Inf".
>
> However, since log10() switches from a numeric answer to "Inf"
> between 1/(10^308)) and 1/(10^309), one possibility for
> reporting such a result is to report "> 308):
>
>  -log10(1/(10^307))
>  # [1] 307
>  -log10(1/(10^308))
>  # [1] 308
>  -log10(1/(10^309))
>  # [1] Inf
>
> Note that the above forces R to compute the number before
> applying log10() to it. You can get a bit further with:
>
>  -log10(1e-322)
>  # [1] 322.0052
>  -log10(1e-323)
>  # [1] 323.0052
>  -log10(1e-324)
>  # [1] Inf
>  -log10(1e-325)
>  # [1] Inf
>
> which may have something to do with R parsing the expression
> before applying log10() to it (I don;t know). However, since
> the p-value returned from an ANOVA will be a number rather
> than an expression, the first set of results is probably more
> relevant to your case.
>
> Hoping this helps,
> Ted.
>
> --------------------------------------------------------------------
> E-Mail: (Ted Harding) <ted.harding@wlandres.net>
> Fax-to-email: +44 (0)870 094 0861
> Date: 28-Aug-11                                       Time: 17:12:34
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>



-- 

Ram H

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