R/classes_rcsv.R

In rossholmberg/rcsv: A custom csv format to encapsulate data frame information into text files. Built around the amazing and fantastic and delicious data.table `fread` and `fwrite` functions

#'
#' @title classes_rcsv
#' @description extract column classes from an rcsv file
#' @details  extract column classes from an rcsv file without loading
#' the entire file into memory
#'
#' @return named character vector of column classes
#'
#' @param file file path from which the rscv will be read
#'
#' @export


classes_rcsv <- function( file ) {
    # open a connection to the file
    con <- file( file, "r" )

    # read in a single line, this will contain the number of header lines
    head.line <- readLines( con = con, n = 1 )

    # check for the tag verifying this file as an rcsv file
    if( !grepl( "rcsvHeader", head.line ) ) {
        stop( "This is not an rcsv file, consider using a different file reader." )
    }

    colref.lines <- as.integer( gsub( ".*colreflines:|}.*", "", head.line ) )
    notes.lines.num <- as.integer( gsub( ".*noteslines:|}.*", "", head.line ) )

    notes <- readLines( con = con, n = notes.lines.num )

    # read in the header, and close the file connection
    header <- readLines( con = con, n = colref.lines )
    close( con )

    # extract the column classes from the header information
    column.classes <- gsub( ".*colclass:|}.*", "", header )
    names( column.classes ) <- gsub( ".*colname:|}.*", "", header )

    return( column.classes )
}