Outline of a more convenient i/o function for R

readwrite.R

# call package easyio

library('foreign')
library('tools')
# library('haven') # for spss (sav, por), stata (dta), sas
#library('memisc') # for `spss.portable.file` and `spss.system.file`
#library('hmisc') # for `spss.get`
#library('openxlsx') # for `read.xlsx`
#library('data.table') # for fread

# matlab i/o: http://cran.r-project.org/web/packages/R.matlab/index.html

# netcdf
# hdf
# maybe: http://cran.r-project.org/web/packages/ncdf4/ncdf4.pdf

# images raster, tif, jpeg

# source a .R file?

# zip, tar, gz, etc.

dataframeToXML <- function(x){
    if(!is.list(x))
        stop("'x' must be a data.frame or list of data.frames")
    if(is.data.frame(x)){
        out <- newXMLNode('data.frame')
        addAttributes(out, name=as.character(substitute(x)))
        for(i in 1:nrow(x)){
            thisrow <- newXMLNode('row')
            addAttributes(thisrow, number=i)
            tmp <- mapply(function(a,b)
                newXMLNode(b,a), x[i,], names(x)
            )
            addChildren(thisrow, tmp)
            addChildren(out, thisrow)
        }
        return(out)
    } else {
        # something to parse a list to XML
        out <- newXMLNode('list')
        addChildren(out, lapply(x, dataframeToXML))
    }
}


readwrite <- function(in, out=NULL, in_fun=NULL, out_fun=NULL, in_opts=NULL, out_opts = NULL, verbose = FALSE, ...){
    
    if(!is.data.frame(in)){
        
        # check in-file size to determine whether to use 
        info <- file.info(in)
        if(info$isdir)
            stop("Value specified for 'in' is a directory, not a file.")
        
        # info$size # use this to suggest `data.table::fread` on large files
        
        # determine in-file type from name
        if(is.null(in_fun)){
            if(in=='clipboard') {
                if(.Platform$OS.type=='windows'){
                    in <- readClipboard()
                    # needs to have a format argument: 1 = text; 2 = DIF
                    # need in_fun to parse character string
                }
                # else unix: file("X11_clipboard")
                # else OSX: pipe("pbpaste")
                if(is.null(in_fun))
                    stop("Must specify 'in_fun' for reading from clipboard.")
            } else {
                ext <- file_ext(in)
                infuns <- list( 'csv' = read.csv,
                                'tsv' = read.delim,
                                'txt' = read.fwf,
                                'Rdata' = load,
                                'rds' = readRDS,
                                'dif' = read.dif, # from utils
                                'dta' = read.dta,
                                'arff' = read.arff,
                                'dbf' = read.dbf,
                                'rec' = read.epiinfo,
                                'mtp' = read.mtp,
                                'mat' = read.octave,
                                'sav' = read.spss, # but maybe something else
                                'por' = spss.portable.file, # but maybe something else???
                                'syd' = read.systat,
                                'xpt' = read.xport,
                                'xlsx' = read.xlsx, # from `openxlsx`
                                'ods' = read.gnumeric.sheet, # library('gnumeric')
                                'ods' = read.ods # from `ROpenOffice` on OmegaHat
                                'json' = fromJSON # from RJSONIO
                                )
                if(ext %in% names(infuns))
                    in_fun <- switch(ext, infuns)
                else
                    in_fun <- readLines
            }
        }
    
    }
    
    # determine out-file type from name
    if(!is.null(out) && is.null(out_fun)){
        if(in=='clipboard') {
            stop("If ")
            if(.Platform$OS.type=='windows') {
                out_fun <- writeClipboard
                # transform `in` to a character string representation
                # writeClipboard needs to have a format argument: 1 = text; 2 = DIF
            }
            # else unix: ??? 
            # else OSX: pipe("pbcopy", "w")
            if(is.null(out_fun))
                stop("Must specify 'out_fun' for reading from clipboard.")
        } else {
            ext <- file_ext(out)
            outfuns <- list('csv' = write.csv,
                            'tsv' = write.delim,
                            'Rdata' = save,
                            'rds' = writeRDS,
                            'arff' = write.arff,
                            'dbf' = write.dbf,
                            'dta' = write.dta,
                            'xpt' = write.xport,
                            'json' = toJSON, # RJSONIO?
                            #'xml' =  # something to build an XML tree
                            )
            if(ext %in% names(outfuns))
                out_fun <- switch(ext, outfuns)
            else
                out_fun <- write.table
        }
    }
    
    
    # read file in
    if(is.data.frame(in))
        obj <- in
    else
        obj <- do.call(in_fun, c(file=in, in_opts))
    
    # write file out
    if(!is.null(out))
        do.call(out_fun, c(file=out, in_opts))
    else
        return(obj)
}


.RdArgs <- function(fun){
    # parse an Rd file and extract details of function arguments to display via `readhelp` and `writehelp`
}

readhelp <- function(file, ...) {
    # use filename to determine default behavior of readwrite
    # display information to the user about the default function by parsing the Rd file
}

writehelp <- function(file, ...) {
    # use filename to determine default behavior of readwrite
    # display information to the user about the default function by parsing the Rd file
}