[R] Counting NA?

[ripley@stats.ox.ac.uk]

On Wed, 23 Oct 2002, Matej Cepl wrote:

> Hi,
>
> how to do quickly equivalent of the following?
>
> 	counter = 0
> 	for(i in 1:length(data$S2)) {
> 		if(!is.na(data$S2[i])) {
> 			counter = counter + 1
> 		}
> 	}
>
> I have imagined something like length(x,na.rm=TRUE).

sum(is.na(data$s2)), using that the fact that TRUE/FALSE are coerced to
1/0.

> How can I get values usually taken from tables like z-score,
> values of t distribution etc.? I could not find them among
> values mentioned in info file.

Use qnorm/pnorm etc.  Here's the examples from chapter 1 of MASS4 (a good
reference!)

The \s. environment includes the equivalent of a comprehensive set of
statistical tables; one can work out $P$ values or critical values for
a wide range of distributions (see Table~\ref{tab:dist.1} on
page~\pageref{tab:dist.1}).
\begin{session}
1 - pf(4.3781, 4, 76)&$P$ value from the ANOVA table above.\cr
qf(0.95, 4, 76)&corresponding 5\% critical point.\cr
\end{session}

In R you could also use

pf(4.3781, 4, 76, lower.tail=FALSE)

although I tend to find that too much typing.

-- 
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 272860 (secr)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595

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