LaF (version 0.5)

laf_open_fwf: Create a connection to a fixed width file.

Description

A connection to the file filename is created. Column types have to be specified. These are not determined automatically as for example read.fwf does. This has been done to increase speed.

After the connection is created data can be extracted using indexing (as in a normal data.frame) or methods such as read_lines and next_block can be used to read in blocks. For processing the file in blocks the (faster) convenience function process_blocks can be used.

Usage

laf_open_fwf(filename, column_types, column_widths, 
    column_names = paste("V", seq_len(length(column_types)), sep = ""), 
    dec = ".", trim=TRUE)

Arguments

filename

character containing the filename of the CSV-file.

column_types

character vector containing the types of data in each of the columns. Valid types are: double, integer, categorical and string.

column_widths

numeric vector containing the width in number of character of each of the columns.

column_names

optional character vector containing the names of the columns.

dec

optional character specifying the decimal mark.

trim

optional logical specifying whether or not whitespace at the end of factor levels or character strings should be trimmed.

Value

• Object of type laf. Values can be extracted from this object using indexing, and methods such as read_lines, next_block.

See Also

See read.fwf for conventional access of fixed width files.

Examples

##---- Should be DIRECTLY executable !! ----
##-- ==>  Define data, use random,
##--	or do  help(data=index)  for the standard data sets.

## The function is currently defined as
function(filename, column_types, column_widths,
        column_names = paste("V", seq_len(length(column_types)), sep=""),
        dec = ".") {
    # check filename
    if (!is.character(filename))
        stop("filename should be of type character.")
    filename <- as.character(filename[1])
    if (!file_access(filename))
	stop("Can not access file '", filename, "'.")
    # check column_types
    types <- laf_to_typecode(column_types)
    # check column widths
    if (!is.numeric(column_widths))
        stop("column_widths should be of type numeric.")
    if (length(column_widths) != length(column_types))      
        stop("Lengths of column_widths and column_types do not match.")
    column_widths <- as.integer(column_widths)
    # check column_names
    if (!is.character(column_names))
        stop("column_names should be of type character.")
    if (length(column_names) != length(column_types))
        stop("Lengths of column_names and column_types do not match.")
    column_names <- make.names(column_names, unique=TRUE)
    # check dec
    if (!is.character(dec))
        stop("dec should be of type character")
    dec <- dec[1]
    if (nchar(dec) != 1)
        stop("The number of characters in dec is not equal to one.")
    # open file
    p <- .Call("laf_open_fwf", filename, types, column_widths, dec)
    # create laf-object
    result <- new(Class="laf", 
        file_id = as.integer(p),
        filename = filename, 
        file_type = "fwf",
        column_types = types,
        column_names = column_names,
        column_widths = column_widths
    )
    return(result)
  }