% This file is part of the 'foreign' package for R
% It is distributed under the GPL version 2 or later

\name{write.dta}
\alias{write.dta}
\title{Write Files in Stata Binary Format}
\usage{
write.dta(dataframe, file, version = 6,
          convert.dates = TRUE, tz = "GMT",
          convert.factors = c("labels", "string", "numeric", "codes"))
}
\arguments{
  \item{dataframe}{a data frame.}
  \item{file}{character string giving filename.}
  \item{version}{Stata version: 6 and 7 are supported.}
  \item{convert.dates}{Convert \code{POSIXt} objects to Stata dates?}
  \item{tz}{timezone for date conversion}
  \item{convert.factors}{how to handle factors}
  } 
\description{
  Writes the data frame to file in the Stata version 6.0 or 7.0 binary
  format.  Does not write matrix variables.
}
\details{
  The major differences between Stata versions is that 7.0 allows 32-character
  variable names. The \code{abbreviate} function is used to trim long
  variables to the permitted length. A warning is given if this is needed and
  it is an error for the abbreviated names not to be unique.

  The columns in the data frame become variables in the Stata data set.
  Missing values are correctly handled.  Optionally, R date/time objects
  (\code{POSIXt} classes) are converted into the Stata format.  This loses
  information -- Stata dates are in days since 1960-1-1.  \code{POSIXct}
  objects can be written without conversion but will not be understood as
  dates by Stata;  \code{POSIXlt} objects cannot be written without
  conversion.

  There are four options for handling factors. The default is to use
  Stata \code{value labels} for the factor levels.
  With \code{convert.factors="string"}, the factor levels are written as
  strings. With \code{convert.factors="numeric"} the numeric values
  of the levels are written, or \code{NA} if they cannot be coerced to
  numeric. Finally, \code{convert.factors="codes"} writes the underlying
  integer codes of the factors. This last used to be the only available
  method and is provided largely for backwards compatibility.

  For Stata 8 or 9 use \code{version=7} -- the only advantage of Stata 8
  format is that it can represent multiple different missing value
  types, and R doesn't have them.
  }
\value{
  \code{NULL}
}
\references{
  Stata 6.0 Users Manual, Stata 7.0 Programming manual, Stata 8.0, 9.0 online
  help describe the file formats.
} 
\author{Thomas Lumley}
\seealso{
  \code{\link{read.dta}},
  \code{\link{attributes}},
  \code{\link{DateTimeClasses}},
  \code{\link{abbreviate}}
}
\examples{
write.dta(swiss, swissfile <- tempfile())
read.dta(swissfile)
}
\keyword{file}
