read.table               package:utils               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 = !stringsAsFactors,
                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 = "#",
                allowEscapes = FALSE, flush = FALSE,
                stringsAsFactors = default.stringsAsFactors(),
                encoding = "unknown")

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

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

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

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

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 readable text-mode
          'connection' (which will be opened for reading if necessary,
          and if so 'close'd (and hence destroyed) at the end of the
          function call).  (If 'stdin()' is used, the prompts for lines
          may be somewhat confusing.  Terminate input with a blank line
          or an EOF signal, 'Ctrl-D' on Unix and 'Ctrl-Z' on Windows. 
          Any pushback on 'stdin()' will be cleared before return.)

          'file' can also be a complete URL.

          To read a data file not in the current encoding (for example
          a Latin-1 file in a UTF-8 locale or conversely) use a 'file'
          connection setting the 'encoding' argument. 

  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, newlines or carriage
          returns.

   quote: the set of quoting characters. To disable quoting altogether,
          use 'quote = ""'.  See 'scan' for the behaviour on quotes
          embedded in quotes.  Quoting is only considered for columns
          read as character, which is all of them unless 'colClasses'
          is specified.

     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. Missing or
          'NULL' 'row.names' generate row names that are considered to
          be 'automatic' (and not preserved by 'as.matrix'). 

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 the
          conversion of columns not otherwise specified by
          'colClasses'. Its value is either a vector of logicals
          (values are recycled if necessary), or a vector of numeric or
          character indices which specify which columns should not be
          converted to factors.

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

          Note that 'as.is' is specified per column (not per variable)
          and so includes the column of row names (if any) and any
          columns to be skipped. 

na.strings: a character vector of strings which are to be interpreted
          as 'NA' values.  Blank fields are also considered to be
          missing values in logical, integer, numeric and complex
          fields.

colClasses: character.  A vector of classes to be assumed for the
          columns.  Recycled as necessary, or if the character vector
          is named, unspecified values are taken to be 'NA'.

          Possible values are 'NA' (when 'type.convert' is used),
          '"NULL"' (when the column is skipped), one of the atomic
          vector classes (logical, integer, numeric, complex,
          character, raw), or '"factor"', '"Date"' or '"POSIXct"'. 
          Otherwise there needs to be an 'as' method (from package
          'methods') for conversion from '"character"' to the specified
          formal class.

          Note that 'colClasses' is specified per column (not per
          variable) and so includes the column of row names (if any). 

   nrows: integer: the maximum number of rows to read in.  Negative and
          other invalid values are ignored.

    skip: integer: 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, and also to ensure that there
          are no duplicates.

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

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.

allowEscapes: logical.  Should C-style escapes such as '\n' be
          processed or read verbatim (the default)?   Note that if not
          within quotes these could be interpreted as a delimiter (but
          not as a comment character).  For more details see 'scan'.

   flush: logical: if 'TRUE', 'scan' will flush to the end of the line
          after reading the last of the fields requested. This allows
          putting comments after the last field.

stringsAsFactors: logical: should character vectors be converted to
          factors?  Note that this is overridden bu 'as.is' and
          'colClasses', both of which allow finer control.

encoding: encoding to be assumed for input strings.  It is used to mark
          character strings as known to be in Latin-1 or UTF-8: it is
          not used to re-encode the input.  For an example of how to do
          so, see the examples under 'file'. 

     ...: Further arguments to be passed to 'read.table'.

Details:

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

     A field or line is 'blank' if it contains nothing (except
     whitespace if no separator is specified) before a comment
     character or the end of the field or line.

     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, so specify 'col.names' if necessary.

     '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 ('read.csv2') 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, and that the comment character is disabled.

     The rest of the line after a comment character is skipped; quotes
     are not processed in comments.  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.

     Quoted fields with embedded newlines are supported except after a
     comment character.

     Note that unless 'colClasses' is specified, all columns are read
     as character columns and then converted.  This means that quotes
     are interpreted in all fields and that a column of values like
     '"42"' will result in an integer 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.  Note that in
     either case tthe columns will logical unless 'colClasses' was
     supplied.

     Character strings in the result (including factor levels) will
     have a declared encoding if 'encoding' is '"latin1"' or '"UTF-8"'.

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 six atomic vector classes.  This can be particularly so when
     reading a column that takes many distinct numeric values, as
     storing each distinct value as a character string can take up to
     14 times as much memory as storing it as an integer.

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

     Using 'comment.char = ""' will be appreciably faster than the
     'read.table' default.

     '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.

References:

     Chambers, J. M. (1992) _Data for models._ Chapter 3 of
     _Statistical Models in S_ eds J. M. Chambers and T. J. Hastie,
     Wadsworth & Brooks/Cole.

See Also:

     The _R Data Import/Export_ manual.

     'scan', 'type.convert', 'read.fwf' for reading _f_ixed _w_idth
     _f_ormatted input; 'write.table'; 'data.frame'.

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

