Read Data Values
Read data into a vector or list from the console or file.
scan(file = "", what = double(), nmax = -1, n = -1, sep = "", quote = if(identical(sep, "\n")) "" else "'\"", dec = ".", skip = 0, nlines = 0, na.strings = "NA", flush = FALSE, fill = FALSE, strip.white = FALSE, quiet = FALSE, blank.lines.skip = TRUE, multi.line = TRUE, comment.char = "", allowEscapes = FALSE, fileEncoding = "", encoding = "unknown", text, skipNul = FALSE)
- the name of a file to read data values from. If the
specified file is
"", then input is taken from the keyboard (or whatever
stdin()reads if input is redirected or R is embedded). (In this case input can be terminated by a blank line or an EOF signal, Ctrl-D on Unix and Ctrl-Z on Windows.)
Otherwise, the file name is interpreted relative to the current working directory (given by
getwd()), unless it specifies an absolute path. Tilde-expansion is performed where supported. When running R from a script,
file = "stdin"can be used to refer to the process's
This can be a compressed file (see
filecan be a
connection, which will be opened if necessary, and if so closed at the end of the function call. Whatever mode the connection is opened in, any of LF, CRLF or CR will be accepted as the EOL marker for a line and so will match
sep = "\n".
filecan also be a complete URL. (For the supported URL schemes, see the URLs section of the help for
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
fileconnection setting its
- the type of
whatgives the type of data to be read. (Here type is used in the sense of
typeof.) The supported types are
whatis a list, it is assumed that the lines of the data file are records each containing
length(what)items (fields) and the list components should have elements which are one of the first six (atomic) types listed or
NULL, see section Details below.
- integer: the maximum number of data values to be read, or if
whatis a list, the maximum number of records to be read. If omitted or not positive or an invalid value for an integer (and
nlinesis not set to a positive value),
scanwill read to the end of
- integer: the maximum number of data values to be read, defaulting to no limit. Invalid values will be ignored.
- by default, scan expects to read white-space
delimited input fields. Alternatively,
sepcan be used to specify a character which delimits fields. A field is always delimited by an end-of-line marker unless it is quoted.
If specified this should be the empty character string (the default) or
NULLor a character string containing just one single-byte character.
- the set of quoting characters as a single character
NULL. In a multibyte locale the quoting characters must be ASCII (single-byte).
- decimal point character. This should be a character string
containing just one single-byte character. (
NULLand a zero-length character vector are also accepted, and taken as the default.)
- the number of lines of the input file to skip before beginning to read data values.
- if positive, the maximum number of lines of data to be read.
- character vector. Elements of this vector are to be
interpreted as missing (
NA) values. Blank fields are also considered to be missing values in logical, integer, numeric and complex fields. Note that the test happens after white space is stripped from the input, so
na.stringsvalues may need their own white space stripped in advance.
- logical: if
scanwill flush to the end of the line after reading the last of the fields requested. This allows putting comments after the last field, but precludes putting more that one record on a line.
- logical: if
scanwill implicitly add empty fields to any lines with fewer fields than implied by
- vector of logical value(s) corresponding to items
whatargument. It is used only when
sephas been specified, and allows the stripping of leading and trailing white space from
numericfields are always stripped). Note: white space inside quoted strings is not stripped.
strip.whiteis of length 1, it applies to all fields; otherwise, if
i-th field is of mode character (because
what[i]is) then the leading and trailing unquoted white space from field
- logical: if
FALSE(default), scan() will print a line, saying how many items have been read.
- logical: if
TRUEblank lines in the input are ignored, except when counting
- logical. Only used if
whatis a list. If
FALSE, all of a record must appear on one line (but more than one record can appear on a single line). Note that using
fill = TRUEimplies that a record will be terminated at the end of a line.
- character: a character vector of length one
containing a single character or an empty string. Use
""to turn off the interpretation of comments altogether (the default).
- logical. Should C-style escapes such as
\n be processed (the default) or read verbatim? Note that if
not within quotes these could be interpreted as a delimiter (but not
as a comment character).
The escapes which are interpreted are the control characters \a, \b, \f, \n, \r, \t, \v and octal and hexadecimal representations like \040 and \0x2A. Any other escaped character is treated as itself, including backslash. Note that Unicode escapes (starting \u or \U: see Quotes) are never processed.
- character string: if non-empty declares the
encoding used on a file (not a connection nor the keyboard) so the
character data can be re-encoded. See the Encoding section
of the help for
file, and the R Data Import/Export Manual.
- encoding to be assumed for input strings. If the
"UTF-8"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 (see
fileEncoding). See also Details.
- character string: if
fileis not supplied and this is, then data are read from the value of
textvia a text connection.
- logical: should nuls be skipped when reading character fields?
The value of
what can be a list of types, in which case
scan returns a list of vectors with the types given by the
types of the elements in
what. This provides a way of reading
columnar data. If any of the types is
NULL, the corresponding
field is skipped (but a
NULL component appears in the result).
The type of
what or its components can be one of the six
atomic vector types or
White space is defined for the purposes of this function as one or more contiguous characters from the set space, horizontal tab, carriage return and line feed. It does not include form feed nor vertical tab, but in Latin-1 and Windows 8-bit locales (but not UTF-8) 'space' includes the non-breaking space "\xa0".
Empty numeric fields are always regarded as missing values.
Empty character fields are scanned as empty character vectors, unless
"" when they are regarded as missing
The allowed input for a numeric field is optional whitespace followed
NA or an optional sign followed by a decimal or
hexadecimal constant (see NumericConstants), or
infinity (ignoring case). Out-of-range values
are recorded as
For an integer field the allowed input is optional whitespace,
followed by either
NA or an optional sign and one or more
digits (0-9): all out-of-range values are converted to
sep is the default (
""), the character \
in a quoted string escapes the following character, so quotes may be
included in the string by escaping them.
sep is non-default, the fields may be quoted in the style of
.csv files where separators inside quotes (
"") are ignored and quotes may be put inside strings by
doubling them. However, if
sep = "\n" it is assumed
by default that one wants to read entire lines verbatim.
Quoting is only interpreted in character fields and in
fields (which might be skipping character fields).
Note that since
sep is a separator and not a terminator,
reading a file by
scan("foo", sep = "\n", blank.lines.skip = FALSE)
will give an empty final line if the file ends in a linefeed and not if
it does not. This might not be what you expected; see also
comment.char occurs (except inside a quoted character
field), it signals that the rest of the line should be regarded as a
comment and be discarded. Lines beginning with a comment character
(possibly after white space with the default separator) are treated as
There is a line-length limit of 4095 bytes when reading from the console (which may impose a lower limit: see An Introduction to R).
There is a check for a user interrupt every 1000 lines if
is a list, otherwise every 10000 items.
file is a character string and
non-default, or if it is a not-already-open connection with a
encoding argument, the text is converted to UTF-8
and declared as such (and the
encoding argument to
is ignored). See the examples of
Embedded nuls in the input stream will terminate the field currently
being read, with a warning once per call to
skipNul = TRUE causes them to be ignored.
whatis a list, a list of the same length and same names (as any) as
what.Otherwise, a vector of the type of
what.Character strings in the result will have a declared encoding if
The default for
multi.line differs from S. To read one record
per line, use
flush = TRUE and
multi.line = FALSE.
(Note that quoted character strings can still include embedded newlines.)
If number of items is not specified, the internal
mechanism re-allocates memory in powers of two and so could use up
to three times as much memory as needed. (It needs both old and new
copies.) If you can, specify either
inputting a large vector, and
inputting a large list.
scan on an open connection to read partial lines can lose
chars: use an explicit separator to avoid this.
nul bytes in fields (including \0 if
allowEscapes = TRUE) may lead to interpretation of the
field being terminated at the
nul. They not normally present
in text files -- see
Becker, R. A., Chambers, J. M. and Wilks, A. R. (1988) The New S Language. Wadsworth & Brooks/Cole.
Quotes for the details of C-style escape sequences.
cat("TITLE extra line", "2 3 5 7", "11 13 17", file = "ex.data", sep = "\n") pp <- scan("ex.data", skip = 1, quiet = TRUE) scan("ex.data", skip = 1) scan("ex.data", skip = 1, nlines = 1) # only 1 line after the skipped one scan("ex.data", what = list("","","")) # flush is F -> read "7" scan("ex.data", what = list("","",""), flush = TRUE) unlink("ex.data") # tidy up ## "inline" usage scan(text = "1 2 3")