read.table               package:base               R Documentation

Data Input

Description:

     Reads a file in table format and creates a data frame from it,
     with cases corresponding to lines and variables to fields in the
     file.

Usage:

     read.table(file, header = FALSE, sep = "", quote = "\"'", dec = ".",
                row.names, col.names, as.is = FALSE, na.strings = "NA",
                colClasses = NA, nrows = -1,
                skip = 0, check.names = TRUE, fill = !blank.lines.skip,
                strip.white = FALSE, blank.lines.skip = TRUE,
                comment.char = "#")

     read.csv(file, header = TRUE, sep = ",", quote="\"", dec=".",
              fill = TRUE, ...)

     read.csv2(file, header = TRUE, sep = ";", quote="\"", dec=",",
              fill = TRUE, ...)

     read.delim(file, header = TRUE, sep = "\t", quote="\"", dec=".",
              fill = TRUE, ...)

     read.delim2(file, header = TRUE, sep = "\t", quote="\"", dec=",",
              fill = TRUE, ...)

Arguments:

    file: the name of the file which the data are to be read from. Each
          row of the table appears as one line of the file.  If it does
          not contain an absolute path, the file name is relative to
          the current working directory, `getwd()'. Tilde-expansion is
          performed where supported.

          Alternatively, `file' can be a `connection', which will be
          opened if necessary, and if so closed at the end of the
          function call.

          `file' can also be a complete URL. 

  header: a logical value indicating whether the file contains the
          names of the variables as its first line.  If missing, the
          value is determined from the file format: `header' is set to
          `TRUE' if and only if the first row contains one fewer field
          than the number of columns.

     sep: the field separator character.  Values on each line of the
          file are separated by this character.  If `sep = ""' (the
          default for `read.table') the separator is ``white space'',
          that is one or more spaces, tabs or newlines.

   quote: the set of quoting characters. To disable quoting altogether,
          use `quote=""'.  See `scan' for the behaviour on quotes
          embedded in quotes.

     dec: the character used in the file for decimal points.

row.names: a vector of row names.  This can be a vector giving the
          actual row names, or a single number giving the column of the
          table which contains the row names, or character string
          giving the name of the table column containing the row names.

          If there is a header and the first row contains one fewer
          field than the number of columns, the first column in the
          input is used for the row names.  Otherwise if `row.names' is
          missing, the rows are numbered.

          Using `row.names = NULL' forces row numbering. 

col.names: a vector of optional names for the variables. The default is
          to use `"V"' followed by the column number.

   as.is: the default behavior of `read.table' is to convert character
          variables (which are not converted to logical, numeric or
          complex) to factors.  The variable `as.is' controls this
          conversion.  Its value is either a vector of logicals (values
          are recycled if necessary), or a vector of numeric indices
          which specify which columns should not be converted to
          factors.

          Note: to suppress all conversions including those of numeric
          columns, set `colClasses = "character"'. 

na.strings: a vector of strings which are to be interpreted as `NA'
          values.  Blank fields are also considered to be missing
          values.

colClasses: character.  A vector of classes to be assumed for the
          columns.  Recycled as necessary.  If this is not one of the
          atomic vector classes (logical, integer, numeric, complex and
          character), there needs to be an `as' method for conversion
          from `"character"' to the specified class, or `NA' when
          `type.convert' is used.

   nrows: the maximum number of rows to read in.  Negative values are
          ignored.

    skip: the number of lines of the data file to skip before beginning
          to read data.

check.names: logical.  If `TRUE' then the names of the variables in the
          data frame are checked to ensure that they are syntactically
          valid variable names.  If necessary they are adjusted (by
          `make.names') so that they are.

    fill: logical. If `TRUE' then in case the rows have unequal length,
          blank fields are implicitly added.

strip.white: logical. Used only when `sep' has been specified, and
          allows the stripping of leading and trailing white space from
          `character' fields (`numeric' fields are always stripped). 
          See `scan' for further details, remembering that the columns
          may include the row names.

blank.lines.skip: logical: if `TRUE' blank lines in the input are
          ignored.

comment.char: character: a character vector of length one containing a
          single character or an empty string.  Use `""' to turn off
          the interpretation of comments altogether.

     ...: Further arguments to `read.table'.

Details:

     If `row.names' is not specified and the header line has one less
     entry than the number of columns, the first column is taken to be
     the row names.  This allows data frames to be read in from the
     format in which they are printed.  If `row.names' is specified and
     does not refer to the first column, that column is discarded from
     such files.

     The number of data columns is determined by looking at the first
     five lines of input (or the whole file if it has less than five
     lines), or from the length of `col.names' if it is specified and
     is longer.  This could conceivably be wrong if `fill' or
     `blank.lines.skip' are true.

     `read.csv' and `read.csv2' are identical to `read.table' except
     for the defaults.  They are intended for reading ``comma separated
     value'' files (`.csv') or the variant used in countries that use a
     comma as decimal point and a semicolon as field separator. 
     Similarly, `read.delim' and `read.delim2' are for reading
     delimited files, defaulting to the TAB character for the
     delimiter.  Notice that `header = TRUE' and `fill = TRUE' in these
     variants.

     Comment characters are allowed unless `comment.char = ""', and
     complete comment lines are allowed provided `blank.lines.skip =
     TRUE' However, comment lines prior to the header must have the
     comment character in the first non-blank column.

Value:

     A data frame (`data.frame') containing a representation of the
     data in the file.  Empty input is an error unless `col.names' is
     specified, when a 0-row data frame is returned: similarly giving
     just a header line if `header = TRUE' results in a 0-row data
     frame.

     This function is the principal means of reading tabular data into
     R.

Note:

     The columns referred to in `as.is' and `colClasses' include the
     column of row names (if any).

     Less memory will be used if `colClasses' is specified as one of
     the five atomic vector classes.

     Using `nrows', even as a mild over-estimate, will help memory
     usage.

     Using `comment.char = ""' will be appreciably faster.

     `read.table' is not the right tool for reading large matrices,
     especially those with many columns: it is designed to read data
     frames which may have columns of very different classes. Use
     `scan' instead.

See Also:

     The R Data Import/Export manual.

     `scan', `type.convert', `read.fwf' for reading fixed width
     formatted input; `read.table.url' for ``reading'' data from the
     internet; `write.table'; `data.frame'.

     `count.fields' can be useful to determine problems with reading
     files which result in reports of incorrect record lengths.

