getXls <- function(
	filename,      #the name of the excel file
	sheet=NULL,    #the name or the number of the sheet to get
	area=NULL,     #the reading area of the chosen sheet
	simplify=FALSE #whether to transform the data to matrix or not
){

if( !any(search()=="package:RODBC") ) {
	lib <- try(library(RODBC), silent=TRUE)
	if(class(lib)=="try-error") { stop("Please install the <RODBC> package from the CRAN.") }
}

con <- odbcConnectExcel(filename)
shnames <- sqlTables(con)$TABLE_NAME
shnames <- substr(shnames, 1, nchar(shnames)-1)
names(shnames) <- as.character(seq(along=shnames))

if( nrow(sqlTables(con))==0 ) { stop( paste("There is no available book named <", filename, ">, or it contains 0 sheet.", sep="") ) }

if(is.null(sheet)) {
	cat("There exist ", length(shnames), " sheets in the excel book.\n\n", sep="")
	print(shnames)
	input <- readline("Hit the number or the name of the sheet you want to import : ")
	cat("\n")

	sheet <- suppressWarnings(as.numeric(input))
	if( is.na(sheet) ) { sheet <- input }
}

if(is.numeric(sheet)) {
	sheet <- shnames[sheet]
}

qry <- paste("select*from [", sheet, "$]", sep="")
tabread <- sqlQuery(con, qry)
odbcClose(con)

if(!is.null(area)) {

	cmpLETTERS <- c(LETTERS, paste(rep(LETTERS, each=26), rep(LETTERS, 26), sep=""))

	fromto <- strsplit(area, ":")[[1]]
	tabcols <- substr(fromto, 1, regexpr("[0-9]", fromto)-1)
	tabcols <- c( which(cmpLETTERS == tabcols[1]), which(cmpLETTERS == tabcols[2]) ) #from "A" to "ZZ" is supported as column indices
	tabcols <- sort(tabcols)
	tabrows <- substring(fromto, regexpr("[0-9]", fromto))
	tabrows <- as.numeric(tabrows)
	tabrows <- sort(tabrows)

	tabread <- tabread[tabrows[1]:tabrows[2], tabcols[1]:tabcols[2]]

}

if(simplify) {
	tabread <- as.matrix(tabread)
}

return(tabread)
}

comment(getXls) <- c(
"getXls - Import MS Excel file using RODBC package.",
"",
"SYNOPSIS",
"    xls <- getXls(filename)",
"INPUT",
"    filename : the name of the excel file (=book) you want to import.",
"    sheet    : the sheet number (or the name) you want to get from the excel book.",
"               You can choose it in the R console if you don't remark this parameter.",
"    area     : character. the reading area designation in excel-like manner.",
"               e.g. 'A1:C20'",
"    simplify : logical. whether to transform the imported data as a matrix.",
"OUTPUT",
"    xls : data.frame or matrix object.",
"",
"See http://www7b.biglobe.ne.jp/~homunculus/r/getXls.html for detailed instruction in Japanese.",
"ver.1.02, written by MOCHI, 2009."
)