\HeaderA{readGAL}{Read a GAL file}{readGAL}
\keyword{IO}{readGAL}
\begin{Description}\relax
Read a GenePix Array List (GAL) file into a dataframe.
\end{Description}
\begin{Usage}
\begin{verbatim}
readGAL(galfile=NULL,path=NULL,header=TRUE,sep="\t",quote="\"",skip=NULL,as.is=TRUE,...)
\end{verbatim}
\end{Usage}
\begin{Arguments}
\begin{ldescription}
\item[\code{galfile}] character string giving the name of the GAL file.  If \code{NULL} then a file with extension \code{.gal} is found in the directory specified by \code{path}.
\item[\code{path}] character string giving the directory containing the files.  If \code{NULL} then assumed to be the current working directory.
\item[\code{header}] logical variable, if \code{TRUE} then the first line after \code{skip} is assumed to contain column headings.  If \code{FALSE} then a value should specified for \code{skip}.
\item[\code{sep}] the field separator character
\item[\code{quote}] the set of quoting characters
\item[\code{skip}] number of lines of the GAL file to skip before reading data.  If \code{NULL} then this number is determined by searching the file for column headings.
\item[\code{as.is}] logical variable, if \code{TRUE} then read in character columns as vectors rather than factors.
\item[\code{...}] any other arguments are passed to \code{read.table}
\end{ldescription}
\end{Arguments}
\begin{Details}\relax
A GAL file is a list of genes IDs and associated information produced by an Axon microarray scanner.
Apart from header information, the file must contain data columns labeled \code{Block}, \code{Column}, \code{Row} and \code{ID}.
A \code{Name} column is usually included as well.
Other columns are optional.
See the Axon URL below for a detaile description of the GAL file format.

This function reads in the data columns with a minimum of user information.
In most cases the function can be used without specifying any of the arguments.
\end{Details}
\begin{Value}
A data frame with columns
\begin{ldescription}
\item[\code{Block}] numeric vector containing the print tip indices
\item[\code{Column}] numeric vector containing the spot columns
\item[\code{Row}] numeric vector containing the spot rows
\item[\code{ID}] character vector, for factor if \code{as.is=FALSE}, containing gene library identifiers
\item[\code{Name}] character vector, for factor if \code{as.is=FALSE}, containing gene names
\end{ldescription}

The data frame will be sorted so that \code{Column} is the fastest moving index, then \code{Row}, then \code{Block}.
\end{Value}
\begin{Author}\relax
Gordon Smyth
\end{Author}
\begin{References}\relax
\url{http://www.axon.com/gn_GenePix_File_Formats.html}
\end{References}
\begin{SeeAlso}\relax
An overview of LIMMA functions for reading data is given in \LinkA{03.ReadingData}{03.ReadingData}.
\end{SeeAlso}
\begin{Examples}
\begin{ExampleCode}
# readGAL()
# will read in the first GAL file (with suffix ".gal")
# found in the current working directory
\end{ExampleCode}
\end{Examples}