\HeaderA{wapply}{Weighted version of the apply function}{wapply}
\keyword{internal}{wapply}
\begin{Description}\relax
A function to perform 'apply' on an matrix of data and corresponding matrix of weights.
\end{Description}
\begin{Usage}
\begin{verbatim}
wapply(X, MARGIN, FUN, W = NULL, ...)
\end{verbatim}
\end{Usage}
\begin{Arguments}
\begin{ldescription}
\item[\code{X}] A matrix of data.
\item[\code{MARGIN}] A vector giving the subscripts which the function will be
applied over. 1 indicates rows, 2 indicates columns.
\item[\code{FUN}] The function to be applied. In the case of functions like
\code{+} the function name must be quoted.
\item[\code{W}] An optional matrix of weights. When \code{W=NULL}, the usual \code{apply} function is called.
\item[\code{...}] optional arguments to \code{FUN}.
\end{ldescription}
\end{Arguments}
\begin{Details}\relax
When weights are provided, these are passed to \code{FUN} along with the data \code{X}. For example, if \code{FUN=meanX}, each data value is multiplied by the corresponding weight before the mean is applied.
\end{Details}
\begin{Value}
If each call to \code{FUN} returns a vector of length \code{n}, then \code{wapply} returns an array of dimension \code{c(n, dim(X)[MARGIN])} if \code{n > 1}. If \code{n = 1}, \code{wapply} returns a vector if \code{MARGIN} has length 1 and an array of dimension \code{dim(X)[MARGIN]} otherwise. If \code{n = 0}, the result has length 0 but not necessarily the "correct" dimension.

If the calls to \code{FUN} return vectors of different lengths, \code{wapply} returns a list of length \code{dim(X)[MARGIN]}.

This function is used in the package \code{multtest} to compute weighted versions of test statistics. It is called by the function \code{get.Tn} inside the user-level function \code{MTP}.
\end{Value}
\begin{Author}\relax
Katherine S. Pollard, \url{http://docpollard.com/}
\end{Author}
\begin{SeeAlso}\relax
\code{\LinkA{get.Tn}{get.Tn}}, \code{\LinkA{MTP}{MTP}}
\end{SeeAlso}
\begin{Examples}
\begin{ExampleCode}
data<-matrix(rnorm(200),nr=20)
weights<-matrix(rexp(200,rate=0.1),nr=20)
wapply(X=data,MARGIN=1,FUN=mean,W=weights)
\end{ExampleCode}
\end{Examples}

