% write.fwf.Rd
%--------------------------------------------------------------------------
% What: Write fixed width format man page
% $Id: write.fwf.Rd 1459 2010-11-12 19:08:12Z warnes $
% Time-stamp: <2008-08-05 12:40:32 ggorjan>
%--------------------------------------------------------------------------

\name{write.fwf}

\alias{write.fwf}

\concept{data output}
\concept{data export}

\title{Write object in fixed width format}

\description{
\code{write.fwf} writes object in *f*ixed *w*idth *f*ormat.
}

\usage{

write.fwf(x, file="", append=FALSE, quote=FALSE, sep=" ", na="",
  rownames=FALSE, colnames=TRUE, rowCol=NULL, justify="left",
  formatInfo=FALSE, quoteInfo=TRUE, width=NULL, eol="\n",
  qmethod=c("escape", "double"),  \dots)

}

\arguments{
  \item{x}{data.frame or matrix, the object to be written}
  \item{file}{character, name of file or connection, look in
    \code{\link{write.table}} for more}
  \item{append}{logical, append to existing data in \code{file}}
  \item{quote}{logical, quote data in output}
  \item{na}{character, the string to use for missing values
    i.e. \code{NA} in the output}
  \item{sep}{character, separator between columns in output}
  \item{rownames}{logical, print row names}
  \item{colnames}{logical, print column names}
  \item{rowCol}{character, rownames column name}
  \item{justify}{character, alignment of character columns; see
    \code{\link{format}}}
  \item{formatInfo}{logical, return information on number of levels,
    widths and format}
  \item{quoteInfo}{logical, should \code{formatInfo} account for quotes}
  \item{width}{numeric, width of the columns in the output}
  \item{eol}{the character(s) to print at the end of each line (row).
    For example, 'eol="\\r\\n"' will produce Windows' line endings on a
    Unix-alike OS, and 'eol="\\r"' will produce files as expected by Mac
    OS Excel 2004.}
  \item{qmethod}{a character string specifying how to deal with embedded
    double quote characters when quoting strings.  Must be one of
    '"escape"' (default), in which case the quote character is
    escaped in C style by a backslash, or '"double"', in which
    case it is doubled.  You can specify just the initial letter.}
  \item{\dots}{further arguments to
    \code{\link{format.info}} and \code{\link{format}}
  }
}

\details{

*F*ixed *w*idth *f*ormat is not used widely anymore. Use some other
format (say *c*omma *s*eparated *v*alues; see \code{\link{read.csv}}) if
you can. However, if you need fixed width format then \code{write.fwf}
can help you.

Output is similar to \code{print(x)} or \code{format(x)}. Formatting is
done completely by \code{\link{format}} on a column basis. Columns in
the output are by default separated with a space i.e. empty column with
a width of one character, but that can be changed with \code{sep}
argument as passed to \code{\link{write.table}} via \dots.

As mentioned formatting is done completely by
\code{\link{format}}. Arguments can be passed to \code{format} via
\code{\dots} to further modify the output. However, note that the
returned \code{formatInfo} might not properly account for this, since
\code{\link{format.info}} (which is used to collect information about
formatting) lacks the arguments of \code{\link{format}}.

\code{quote} can be used to quote fields in the output. Since all
columns of \code{x} are converted to character (via
\code{\link{format}}) during the output, all columns will be quoted! If
quotes are used, \code{\link{read.table}} can be easily used to read the
data back into \R. Check examples. Do read the details about
\code{quoteInfo} argument.

Use only *true* character, i.e., avoid use of tabs, i.e., "\\t", or similar
separators via argument \code{sep}. Width of the separator is taken as
the number of characters evaluated via \code{\link{nchar}(sep)}.

Use argument \code{na} to convert missing/unknown values. Only single value
can be specified. Use \code{\link{NAToUnknown}} prior to export if you need
greater flexibility.

If \code{rowCol} is not \code{NULL} and \code{rownames=TRUE}, rownames
will also have column name with \code{rowCol} value. This is mainly for
flexibility with tools outside \R. Note that (at least in \R 2.4.0) it
is not "easy" to import data back to \R with \code{\link{read.fwf}} if
you also export rownames. This is the reason, that default is
\code{rownames=FALSE}.

Information about format of output will be returned if
\code{formatInfo=TRUE}. Returned value is described in value
section. This information is gathered by \code{\link{format.info}} and
care was taken to handle numeric properly. If output contains rownames,
values account for this. Additionally, if \code{rowCol} is not
\code{NULL} returned values contain also information about format
of rownames.

If \code{quote=TRUE}, the output is of course wider due to
quotes. Return value (with \code{formatInfo=TRUE}) can account for this
in two ways; controlled with argument \code{quoteInfo}. However, note
that there is no way to properly read the data back to \R if
\code{quote=TRUE & quoteInfo=FALSE} arguments were used for
export. \code{quoteInfo} applies only when \code{quote=TRUE}. Assume
that there is a file with quoted data as shown bellow (column numbers in
first three lines are only for demonstration of the values in the
output).

\preformatted{
123456789 12345678 # for position
123 1234567 123456 # for width with quoteInfo=TRUE
 1   12345   1234  # for width with quoteInfo=FALSE
"a" "hsgdh" "   9"
" " "   bb" " 123"
}

With \code{quoteInfo=TRUE} \code{write.fwf} will return

\preformatted{
colname position width
V1             1     3
V2             5     7
V3            13     6
}

or (with \code{quoteInfo=FALSE})

\preformatted{
colname position width
V1             2     1
V2             6     5
V3            14     4
}

Argument \code{width} can be used to increase the width of the columns
in the output. This argument is passed to the width argument of
\code{\link{format}} function. Values in \code{width} are recycled if
there is less values than the number of columns. If the specified width
is to short in comparison to the "width" of the data in particular
column, error is issued.

}

\value{

Besides its effect to write/export data \code{write.fwf} can provide
information on format and width. A data.frame is returned with the
following columns:
  \item{colname}{name of the column}
  \item{nlevels}{number of unique values (unused levels of factors are
    dropped), 0 for numeric column}
  \item{position}{starting column number in the output}
  \item{width}{width of the column}
  \item{digits}{number of digits after the decimal point}
  \item{exp}{width of exponent in exponential representation; 0 means
    there is no exponential representation, while 1 represents exponent
    of length one i.e. \code{1e+6} and 2 \code{1e+06} or \code{1e+16}}
}

\author{Gregor Gorjanc}

\seealso{
  \code{\link{format.info}}, \code{\link{format}},
  \code{\link{NAToUnknown}}, \code{\link{write.table}},
  \code{\link{read.fwf}}, \code{\link{read.table}} and
  \code{\link{trim}}
}

\examples{

  ## Some data
  num <- round(c(733070.345678, 1214213.78765456, 553823.798765678,
                 1085022.8876545678,  571063.88765456, 606718.3876545678,
                 1053686.6, 971024.187656, 631193.398765456, 879431.1),
               digits=3)

  testData <- data.frame(num1=c(1:10, NA),
                         num2=c(NA, seq(from=1, to=5.5, by=0.5)),
                         num3=c(NA, num),
                         int1=c(as.integer(1:4), NA, as.integer(4:9)),
                         fac1=factor(c(NA, letters[1:9], "hjh")),
                         fac2=factor(c(letters[6:15], NA)),
                         cha1=c(letters[17:26], NA),
                         cha2=c(NA, "longer", letters[25:17]),
                         stringsAsFactors=FALSE)
  levels(testData$fac1) <- c(levels(testData$fac1), "unusedLevel")
  testData$Date <- as.Date("1900-1-1")
  testData$Date[2] <- NA
  testData$POSIXt <- as.POSIXct(strptime("1900-1-1 01:01:01",
                                         format="\%Y-\%m-\%d \%H:\%M:\%S"))
  testData$POSIXt[5] <- NA

  ## Default
  write.fwf(x=testData)

  ## NA should be -
  write.fwf(x=testData, na="-")
  ## NA should be -NA-
  write.fwf(x=testData, na="-NA-")

  ## Some other separator than space
  write.fwf(x=testData[, 1:4], sep="-mySep-")

  ## Force wider columns
  write.fwf(x=testData[, 1:5], width=20)

  ## Write to file and report format and fixed width information
  file <- tempfile()
  formatInfo <- write.fwf(x=testData, file=file, formatInfo=TRUE)

  ## Read exported data back to R (note +1 due to separator)
  ## ... without header
  read.fwf(file=file, widths=formatInfo$width + 1, header=FALSE, skip=1,
           strip.white=TRUE)

  ## ... with header - via postimport modfication
  tmp <- read.fwf(file=file, widths=formatInfo$width + 1, skip=1,
                  strip.white=TRUE)
  colnames(tmp) <- read.table(file=file, nrow=1, as.is=TRUE)
  tmp

  ## ... with header - persuading read.fwf to accept header properly
  ## (thanks to Marc Schwartz)
  read.fwf(file=file, widths=formatInfo$width + 1, strip.white=TRUE,
           skip=1, col.names=read.table(file=file, nrow=1, as.is=TRUE))

  ## ... with header - with the use of quotes
  write.fwf(x=testData, file=file, quote=TRUE)
  read.table(file=file, header=TRUE, strip.white=TRUE)

  ## Tidy up
  unlink(file)
}

\keyword{print}
\keyword{file}

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% write.fwf.Rd ends here