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% File src/library/base/man/data.matrix.Rd
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% Part of the R package, http://www.R-project.org
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% Copyright 1995-2008 R Core Team
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% Distributed under GPL 2 or later
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\name{data.matrix}
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\alias{data.matrix}
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\title{Convert a Data Frame to a Numeric Matrix}
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\description{
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  Return the matrix obtained by converting all the variables in a data
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  frame to numeric mode and then binding them together as the columns of
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  a matrix.  Factors and ordered factors are replaced by their internal
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  codes.
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}
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\usage{
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data.matrix(frame, rownames.force = NA)
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}
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\arguments{
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  \item{frame}{a data frame whose components are logical vectors,
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    factors or numeric vectors.}
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  \item{rownames.force}{logical indicating if the resulting matrix
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    should have character (rather than \code{NULL})
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    \code{\link{rownames}}.  The default, \code{NA}, uses \code{NULL}
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    rownames if the data frame has \sQuote{automatic} row.names or for a
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    zero-row data frame.}
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}
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\details{
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  Logical and factor columns are converted to integers.  Any other
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  column which is not numeric (according to \code{\link{is.numeric}}) is
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  converted by \code{\link{as.numeric}} or, for S4 objects,
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  \code{\link{as}(, "numeric")}.  If all columns are integer (after
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  conversion) the result is an integer matrix, otherwise a numeric
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  (double) matrix.
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}
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\value{
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  If \code{frame} inherits from class \code{"data.frame"}, an integer or
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  numeric matrix of the same dimensions as \code{frame}, with dimnames
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  taken from the \code{row.names} (or \code{NULL}, depending on
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  \code{rownames.force}) and \code{names}.
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  Otherwise, the result of \code{\link{as.matrix}}.
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}
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\note{
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  The default behaviour for data frames differs from \R < 2.5.0 which
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  always gave the result character rownames.
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}
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\seealso{
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  \code{\link{as.matrix}},
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  \code{\link{data.frame}},
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  \code{\link{matrix}}.
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}
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\references{
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  Chambers, J. M. (1992)
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  \emph{Data for models.}
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  Chapter 3 of \emph{Statistical Models in S}
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  eds J. M. Chambers and T. J. Hastie, Wadsworth & Brooks/Cole.
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}
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\examples{
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DF <- data.frame(a = 1:3, b = letters[10:12],
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                 c = seq(as.Date("2004-01-01"), by = "week", len = 3),
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                 stringsAsFactors = TRUE)
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data.matrix(DF[1:2])
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data.matrix(DF)
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}
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\keyword{array}