[R] Counting NA?
ripley@stats.ox.ac.uk
ripley at stats.ox.ac.uk
Wed Oct 23 12:14:47 CEST 2002
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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